=head1 名前 perlguts - Perl API への誘い =head1 説明 このドキュメントでは Perl コアの基本的な動作に付いてのいくつかの情報を 含むと共に, Perl API をどのように使うのかに付いて記述しています. まだまだ完全というわけでもなく, また間違った記述を含むことも あるかもしれません. 疑問やコメントは後述の著者に連絡してください. =head1 変数 =head2 データタイプ Perl には３つの主なデータタイプを処理する為の３つの typedef があります: SV Scalar Value AV Array Value HV Hash Value SV スカラー値 AV 配列値 HV ハッシュ値 各 typedef はその操作のために特定の関数を持っています. =head2 "IV" とは. Perl は(整数と同様に)ポインタを保持するのにも十分な大きさを保証する 単純な符号付き整数である特別な typedef, IV を使います. もう一つ符号無しの IV として UV もあります. また, I32 及び I16 という２つの特別な typedef ももっていて, それぞれ 少なくとも 32-bit 及び 16-bit 長があります. (そして同様に U32, U16 も.) これらは通常はぴったり 32 及び 16 ビット長ですが, Crays では両方とも 64 ビットです. =head2 SVの使い方 SV は１つのコマンドで生成及びロードできます. ５種類の値がロード 可能です: 整数値(IV), 符号なし整数値(UV), 倍精度浮動小数点数 (NV), 文字列 (PV), そして別のスカラー (SV). ７つのルーチンがあります: SV* newSViv(IV); SV* newSVuv(UV); SV* newSVnv(double); SV* newSVpv(const char*, STRLEN); SV* newSVpvn(const char*, STRLEN); SV* newSVpvf(const char*, ...); SV* newSVsv(SV*); C は perl が処理できる文字列の大きさを表現するのに十分な 大きさを保証する整数型(Size_t, 通常 F で size_t として 定義されています)です. あまりありませんが SV により複雑な初期化を行い必要があるようなケース では, newSV(len) を使って空っぽの SV を作ることも出来ます. C が 0 の時には NULL 型である空っぽの SV が, そうでなければ SvPVX でアクセス できる len + 1 (NUL用) バイトの領域を確保した PV 型の SV が返されます. どちらの時も SV の値は undef です. SV *sv = newSV(0); /* no storage allocated */ SV *sv = newSV(10); /* 10 (+1) bytes of uninitialised storage allocated */ SV *sv = newSV(0); /* 記憶領域なし */ SV *sv = newSV(10); /* 初期化されていない 10 (+1) バイトの領域を確保 */ I<既に存在する> SV の値を変更するには以下の８つのルーチンがあります: void sv_setiv(SV*, IV); void sv_setuv(SV*, UV); void sv_setnv(SV*, double); void sv_setpv(SV*, const char*); void sv_setpvn(SV*, const char*, STRLEN) void sv_setpvf(SV*, const char*, ...); void sv_vsetpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool *); void sv_setsv(SV*, SV*); C, C, 若しくは C を使うことで設定する 文字列の長さを指定も出来舞うし, C を使って若しくは C の２つめの引数のように 0 を指定することで Perl に長さを計算させることも出来ます. C の引数は C の用の処理され, 整形された 出力が値となります. C は C と似ていますが, 可変長引数への ポインタかアドレスと SV の配列の長さのどちらかを指定できます. 最後の引数は真偽値へのポインタで, 戻った時にその値が真であれば 文字列の整形にロケール情報が使われ, 文字列の中身はその結果信頼 できません (L 参照). その情報が重要でなければ NULL を 渡すことも出来ます. この関数はフォーマットの長さを指定する必要がある 点に注意してください. C 関数は一般的に "magic" を持っている値に対する処理には 十分ではありません. このドキュメントで後述する L<< |/マジック仮想テーブル >> を参照して ください. 文字列を格納している全ての SV では NUL 文字で終端するべきです. もし NUL 終端がされていないとNUL終端された文字列を 前提としているC関数やシステムコールに渡したときにコアダンプや 破損のリスクを負うことになります. Perl の関数はこの理由から大抵 NUL を追加しています. しかしそれでも SV に格納されている文字列を C 関数やシステムコールに 渡すときには十分に注意する必要があります. SV が指し示している実際の値にアクセスするためには次のマクロを使い: SvIV(SV*) SvUV(SV*) SvNV(SV*) SvPV(SV*, STRLEN len) SvPV_nolen(SV*) これらは実際のスカラーの型を IV, UV, double, 若しくは文字列へと 自動的に強制します. C マクロでは, 文字列の長さは変数 C で示す場所へと返され ます(これはマクロなので C<&len> はつかいまI<せん>). もしデータの 長さが不要であれば, C マクロを使います. 歴史的には この用途として C マクロにグローバル変数 C を渡して いました. しかしこれは C はスレッド Perl ではスレッド ローカルストレージにアクセス縷々為とても非効率でした. どのような ケースでも, Perl は NUL を含んでいたり又は NUL で終端していないと いった任意の文字列を許可していることを覚えておいてください. また C では C と安心して書くことを 許可していない点も思い出しておいてください. あなたのコンパイラでは 動くかもしれませんが, 全ての環境でそうとはかぎりません. こういった文は分けて書くようにしてください: SV *s; STRLEN len; char * ptr; ptr = SvPV(s, len); foo(ptr, len); スカラーの値が TRUE であるかを知りたいときには次の関数を使います: SvTRUE(SV*) Perl は文字列を自動的に拡張しますが, Perl に SV 用にもっと多くの メモリを確保させたいときには次のマクロを使います: SvGROW(SV*, STRLEN newlen) これはもっと多くのメモリを割り当てる必要がありかを決定します. もし必要であればこれは関数 C を呼び出します. C は SV に割り当てられているメモリの増加だけを行って減少はさせない点に 注意してください, そして後続の NUL の為のバイトは自動的に追加されない 点にも注意してください(perl の文字列関数は通常 C を行います). もう持っている SV が Perl の考える何の種類のデータが入っているのかを 知りたいときには以下のマクロで SV の種類を調べることが出来ます. SvIOK(SV*) SvNOK(SV*) SvPOK(SV*) SV に格納されている文字列の長さを取得及び設定するには次のマクロを使います: SvCUR(SV*) SvCUR_set(SV*, I32 val) SV に格納されている文字列の末尾へのポインタも次のマクロで取得できます: SvEND(SV*) しかしこの３つのマクロは C が真の時のみ有効な点に注意して ください. C に格納されている文字列の末尾に何かを追加したいときには 以下の関数を使います: void sv_catpv(SV*, const char*); void sv_catpvn(SV*, const char*, STRLEN); void sv_catpvf(SV*, const char*, ...); void sv_vcatpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool); void sv_catsv(SV*, SV*); １つめの関数は追加される文字列の長さを C を使って計ります. ２つめの関数では文字列の長さを自分で指定します. ３つめの関数では その引数を C のように処理してその整形結果を追加します. ４つめの関数は C の用に動作します. va_list 引数の代わりに SVの配列のアドレスと長さを指定することも出来ます. ５つめの関数は １つめのSVに格納されている文字列を２つめのSVに格納されている文字列で 拡張します. これは２つめのSVを文字列として解釈出来るように強制します. C 関数は"マジック"を持っている値に対する処理としては 一般に十分ではありません. このドキュメントで後述する L<< |/マジック仮想テーブル >> を参照して ください. スカラー変数の名前を知っているときには次のようにしてその SV へのポインタ を取得できます: SV* get_sv("package::varname", FALSE); これは変数が存在しないときには NULL を返します. 変数(若しくは何らかの SV)が実際に C であるかを知りたいときには 次のように呼び出します: SvOK(SV*) スカラーの C 値は C と呼ばれる SV のインスタンス に格納されています. このアドレスは C が必要な時にはいつでも使えます. でも sv と C<&PL_sv_undef> を比較しないでください. Perl のコードで言うと 次の時には動作するでしょう: foo(undef); しかし次の時には動作しません: $x = undef; foo($x); 繰り返しますが, sv が defined であるかを調べるときは常に SvOK() を 使うようにしてください. また, SV や HV の値として C<&PL_sv_undef> を使う時も注意する必要が あります (L<< |/AV と HV と未定義値 >> を参照してください). C と C という２つの値もあり, これらはそれぞれ 真偽値の TRUE と FALSE の値を含んでいます. C と同じように これらのアドレスは C が必要な箇所で使うことが出来ます. C<(SV *) 0> を C<&PL_sv_undef> と同じと思うようなことはしないでください. 次のコードを見てください: SV* sv = (SV*) 0; if (I-am-to-return-a-real-value) { sv = sv_2mortal(newSViv(42)); } sv_setsv(ST(0), sv); これはジスうちを返すべきであれば新しい SV (値 42 を保持) を, そうでなければ undef を返そうとしています. これは NULL ポインタをどこか下の方で 返す代わりにセグメント違反, バスエラー, それか単におかしな結果を 引き起こします. 始めの行にある零を C<&PL_sv_undef> に返ればうまく いきます. 作成した SV を解放するには C を呼び出します. 大抵この呼び出しは必要ないでしょう( L<< |/リファレンスカウンタと揮発属性 >> を参照してください). =head2 オフセット Perl は文字列の始まりから文字を効果的に削除する関数 C を 提供しています. SV と PV の中のどこかを示すポインタを渡すと, そのポインタより前の全てを削除します. その効力は小さな技法に由来します. C は実際に文字を削除するのではなく, C (Offset OK) フラグを 設定します. これにより他の関数にオフセットが有効になっていることを通知します. そして削除されたバイト数を SV の IV フィールドに記します. これにより (C 呼び出しの) PV ポインタはその分前に送られ, C, C も調節されます. この結果, アロケートしたバッファの始点は C の 位置となり, PV ポインタはこの確保した領域の途中を指す様になります. 以下の例でよくわかると思います. % ./perl -Ilib -MDevel::Peek -le '$a="12345"; $a=~s/.//; Dump($a)' SV = PVIV(0x8128450) at 0x81340f0 REFCNT = 1 FLAGS = (POK,OOK,pPOK) IV = 1 (OFFSET) PV = 0x8135781 ( "1" . ) "2345"\0 CUR = 4 LEN = 5 ここで, 切り落とされたバイト数 (1) は IV に置かれ, C はこれがオフセットであることを教えてくれます. "実際の"文字列と "仮装の"文字列の開始との間の部分は括弧で示されていて, C と C は実際の文字列ではなく仮装された文字列の始まりを反映して います. オフセットのハックと同じように, AV にも shift や配列の始まりでの splice で効率的な処理を行っています; C は Perl から見える 配列の中の最初の要素を指しますが, C は C 配列の実際の開始 点を指し示します. この2つは通常は同じですが, C は C を１つ増加させ, C と C を１つ減少することで 処理されます. そしてC配列の実際の開始点は配列を解放するときだけ 使われます(訳注:よくわかんない^^;). F の C を 参照してください. =head2 SVに実際格納されているもの スカラーの型を決定するのに普通使う方法は C マクロを 使うだったことを思い出してください. スカラーには数値と文字列の両方に 慣れるのでこれらのマクロは常に TRUE を返して C マクロは 適切に文字列を整数/doubleへ若しくは整数/doubleを文字列へと変換を 行います. もし SV の中に整数, double, 文字列へのポインタをI<本当に>持って いるかを知りたいのであれば以下の3つのマクロを代わりに使います. SvIOKp(SV*) SvNOKp(SV*) SvPOKp(SV*) これらは SV の中に本当に整数, double, 若しくは文字列ポインタを持っている かを教えてくれます. "p" は private を示しています. プライベートとパブリックのフラグは様々な点で異なります. 例えば, tie された SV は IV スロットに正しい値を持っている (つまり SvIOKp は真)かもしれませんが, データは直接ではなく FETCH を 通してアクセスするべきであるため, SvIOK は偽になります. 他にも, 数値変換が起こって精度が失われたときにはプライベートフラグは'不可逆' 値として設定されます. NV が精度を落として IV に変換されたときには, SvIOKp, SvNOKp, そして SvNOK は設定されますが, SvIOK は設定されません. 一般的には, それでも, C マクロを使うのが最善です. =head2 AVの使い方 AV を作成してロードするには2つのやり方があります. 1つめは空のAVを作る 方法です: AV* newAV(); 2つめの方法ではAVを作ってそれをSVで初期化させます: AV* av_make(I32 num, SV **ptr); 2つめの引数は C 個の C を含んでいる配列へのポインタです. AV が作成された後には SV は望むであれば破棄できます. AV を作った後には AV に対して次の操作を行うことが出来ます. void av_push(AV*, SV*); SV* av_pop(AV*); SV* av_shift(AV*); void av_unshift(AV*, I32 num); これらは C の例外をおいておけばよく似た操作です. これは配列の先頭に C 個の C 値を挿入します. これらの新しい要素に対して値を設定するためには C (後述) を 使います. 他の関数もあります: I32 av_len(AV*); SV** av_fetch(AV*, I32 key, I32 lval); SV** av_store(AV*, I32 key, SV* val); C 関数は配列の最大の添字を返します(ちょうど Perl の $#array と同じです). もし配列が空であれば -1 が返されます. C 関数は 添字 C の値を返しますが, C が零でなければ C は 添字の場所に C を格納します. C 関数は添字C の 場所に値 C を格納しますが, C の参照家運tの派増やしません. これは呼び出しもとの責任になります. また C が NULL を返したときには呼び出し元はメモリリークを回避するために参照 カウンタを減少させる必要があります. C と C は 共にその復帰値に C ではなく C を返すことに注意してください. void av_clear(AV*); void av_undef(AV*); void av_extend(AV*, I32 key); C 関数は AV* 配列の全ての要素を削除しますが, 配列そのものは 削除しません. C は全ての要素と配列自身を削除します. C 関数は配列を拡張して少なくとも C 要素を 格納できるようになります. もし C が配列が現在確保している 長さよりも短いときにはなにも行いません. 文字配列の変数名を知っているのなら次のようにしてその AV への ポインタを取得できます: AV* get_av("package::varname", FALSE); これは変数が存在しないときには NULL を返します. tie された配列に対しての配列アクセス関数の使い方は L<< |/tie されたハッシュと配列のマジックの理解 >> を参照してください. =head2 HVの使い方 HVを作るには次の関数を使います: HV* newHV(); HVを生成した後はHVに対して以下の操作を行えます: SV** hv_store(HV*, const char* key, U32 klen, SV* val, U32 hash); SV** hv_fetch(HV*, const char* key, U32 klen, I32 lval); C パラメータは渡されたキーの長さです(Perlがキーの長さを測ってくれることを 期待して0を渡すことはできないことに注意してください). C 引数には 格納するスカラーを指すSVポインタを渡します. C には計算済みの ハッシュ値を渡します(Cに計算させる場合には0を渡します). (hv_fetchの)C パラメータは取得が実際には格納処理の一環として 行われるかどうかを提示します. これが設定されているときは新しい未定義値が 指定されたキーに対して追加され, 値がさも既に存在していたかのように C から返ります. C 及び C は C ではなく C を返すことに 注意してください. スカラー値にアクセスするためにはこの復帰値をまず デリファレンスする必要があります. またデリファレンスの前に復帰値が NULLではないことを確認するべきです. 以下の２つの関数はハッシュテーブルのエントリが存在するかの確認するもの 及びエントリの削除を行う物です. bool hv_exists(HV*, const char* key, U32 klen); SV* hv_delete(HV*, const char* key, U32 klen, I32 flags); もし C が C フラグを含まないときは C は 削除された値のモータルコピーを作成し返します. その他の関数: void hv_clear(HV*); void hv_undef(HV*); AVでのものと同じように, C はハッシュテーブルの全てのエントリを 削除します. 但しハッシュテーブル自身は削除しません. C は エントリと共にハッシュテーブル自身も削除します. PerlはHEのtypedefと構造体のリンクリストに実際のデータも保持しています. これらは実際のキー及び値のポインタ(それに加えて管理用の追加領域)を含んで います. キーは文字列へのポインタで, 値は C です. しかし一旦 C を 取得すれば実際のキー及び値を取得するために次の関数を使えます. I32 hv_iterinit(HV*); /* Prepares starting point to traverse hash table */ /* ハッシュテーブルの走査(traverse)の開始点を準備 */ HE* hv_iternext(HV*); /* Get the next entry, and return a pointer to a structure that has both the key and value */ /* 次のエントリを取得し, キーと値を持つ構造体への ポインタを返す */ char* hv_iterkey(HE* entry, I32* retlen); /* Get the key from an HE structure and also return the length of the key string */ /* HE構造体からキーを取得. キー文字列の長さも返す */ SV* hv_iterval(HV*, HE* entry); /* Return an SV pointer to the value of the HE structure */ /* HE構造体の値へのSVポインタを返す */ SV* hv_iternextsv(HV*, char** key, I32* retlen); /* This convenience routine combines hv_iternext, hv_iterkey, and hv_iterval. The key and retlen arguments are return values for the key and its length. The value is returned in the SV* argument */ /* hv_iternext, hv_iterkey, hv_iterval を一度に行う. key 及び retlen 引数にキー及びキーの長さが返される. 値は SV* 引数に返される. (訳注:復帰値として返されるの 間違い？) */ ハッシュの名前がわかっているのなら次の関数でそのHVへのポインタを 取得できます: HV* get_hv("package::varname", FALSE); 変数が存在しないときは NULL を返します. ハッシュのアルゴリズムは C マクロで 定義されています: hash = 0; while (klen--) hash = (hash * 33) + *key++; hash = hash + (hash >> 5); /* after 5.6 */ 最後のステップはハッシュ値に下位ビットの拡散を進めるためにバージョン 5.6 で追加されました. tie されたハッシュに対してのハッシュアクセス関数の使い方は L<< |/タイされたハッシュと配列のマジックの理解 >> を参照してください. =head2 ハッシュAPIの拡張 バージョン 5.004 から以下の関数がサポートされました: HE* hv_fetch_ent (HV* tb, SV* key, I32 lval, U32 hash); HE* hv_store_ent (HV* tb, SV* key, SV* val, U32 hash); bool hv_exists_ent (HV* tb, SV* key, U32 hash); SV* hv_delete_ent (HV* tb, SV* key, I32 flags, U32 hash); SV* hv_iterkeysv (HE* entry); Note that these functions take C keys, which simplifies writing of extension code that deals with hash structures. These functions also allow passing of C keys to C functions without forcing you to stringify the keys (unlike the previous set of functions). They also return and accept whole hash entries (C), making their use more efficient (since the hash number for a particular string doesn't have to be recomputed every time). See L for detailed descriptions. The following macros must always be used to access the contents of hash entries. Note that the arguments to these macros must be simple variables, since they may get evaluated more than once. See L for detailed descriptions of these macros. HePV(HE* he, STRLEN len) HeVAL(HE* he) HeHASH(HE* he) HeSVKEY(HE* he) HeSVKEY_force(HE* he) HeSVKEY_set(HE* he, SV* sv) These two lower level macros are defined, but must only be used when dealing with keys that are not Cs: HeKEY(HE* he) HeKLEN(HE* he) Note that both C and C do not increment the reference count of the stored C, which is the caller's responsibility. If these functions return a NULL value, the caller will usually have to decrement the reference count of C to avoid a memory leak. =head2 AV と HV と未定義値 Sometimes you have to store undefined values in AVs or HVs. Although this may be a rare case, it can be tricky. That's because you're used to using C<&PL_sv_undef> if you need an undefined SV. For example, intuition tells you that this XS code: AV *av = newAV(); av_store( av, 0, &PL_sv_undef ); is equivalent to this Perl code: my @av; $av[0] = undef; Unfortunately, this isn't true. AVs use C<&PL_sv_undef> as a marker for indicating that an array element has not yet been initialized. Thus, C would be true for the above Perl code, but false for the array generated by the XS code. Other problems can occur when storing C<&PL_sv_undef> in HVs: hv_store( hv, "key", 3, &PL_sv_undef, 0 ); This will indeed make the value C, but if you try to modify the value of C, you'll get the following error: Modification of non-creatable hash value attempted In perl 5.8.0, C<&PL_sv_undef> was also used to mark placeholders in restricted hashes. This caused such hash entries not to appear when iterating over the hash or when checking for the keys with the C function. You can run into similar problems when you store C<&PL_sv_true> or C<&PL_sv_false> into AVs or HVs. Trying to modify such elements will give you the following error: Modification of a read-only value attempted To make a long story short, you can use the special variables C<&PL_sv_undef>, C<&PL_sv_true> and C<&PL_sv_false> with AVs and HVs, but you have to make sure you know what you're doing. Generally, if you want to store an undefined value in an AV or HV, you should not use C<&PL_sv_undef>, but rather create a new undefined value using the C function, for example: av_store( av, 42, newSV(0) ); hv_store( hv, "foo", 3, newSV(0), 0 ); =head2 リファレンス リファレンスはスカラーの特殊な形式です. (リファレンスを含む)ほかのデータ形式を指し示します. リファレンスを作成するには次の関数のいずれかを使います. SV* newRV_inc((SV*) thing); SV* newRV_noinc((SV*) thing); C 引数には C もしくは C, C のいずれかを指定します. この２つの関数は, CがCの参照カウンタ をインクリメントし, C がインクリメントしない点を除いて 同一のものです. 歴史的な経緯から, CはCと同義です. リファレンスが生成された後は, 次のマクロによって リファレンスをデリファレンスできます. SvRV(SV*) そして, 返されたCを必要に応じて C もしくは C に キャストして, 固有のメソッドを呼びます. SV がリファレンスかどうか確かめるには次のマクロを使います: SvROK(SV*) リファレンスがどの種類のものを参照しているのか見つけるためには 次のマクロの復帰値で調べることができます. SvTYPE(SvRV(SV*)) 返されるもののうち, 主なものは次のものです. SVt_IV Scalar SVt_NV Scalar SVt_PV Scalar SVt_RV Scalar SVt_PVAV Array SVt_PVHV Hash SVt_PVCV Code SVt_PVGV Glob (possible a file handle) SVt_PVMG Blessed or Magical Scalar SVt_IV スカラー SVt_NV スカラー SVt_PV スカラー SVt_RV スカラー SVt_PVAV 配列 SVt_PVHV ハッシュ SVt_PVCV コード SVt_PVGV グラブ (ファイルハンドルを含む) SVt_PVMG ブレスもしくはマジックされたスカラー See the sv.h header file for more details. より詳細な情報に関しては sv.h ヘッダファイルを参照してください. =head2 ブレスされたリファレンスとクラスオブジェクト リファレンスはperlのオブジェクト指向プログラミングとしても使われます. オブジェクト指向の語彙のなかにおいて, オブジェクトは単純にパッケージ (もしくはクラス)にブレスされたリファレンスです. 一度ブレスされると, プログラマはリファレンスをクラス内の種々のメソッドへの アクセスに使えます. リファレンスは次の関数によってパッケージに対してブレスされます: SV* sv_bless(SV* sv, HV* stash); C引数はリファレンスでなければなりません. C引数でリファレンスがどのクラスに属するかを指定します. クラス名からスタッシュへの変換については L を 参照してください. /* まだ準備中です */ もしrcがまだリファレンスとしてアップグレードされていなければ, アップグレードされます. rvが指すための新しいSVを作成します. もし C がNULLでなければ, SVは指定したクラスにブレスされます. SVが返されます. SV* newSVrv(SV* rv, const char* classname); Copies integer, unsigned integer or double into an SV whose reference is C. SV is blessed if C is non-null. SV* sv_setref_iv(SV* rv, const char* classname, IV iv); SV* sv_setref_uv(SV* rv, const char* classname, UV uv); SV* sv_setref_nv(SV* rv, const char* classname, NV iv); Copies the pointer value (I) into an SV whose reference is rv. SV is blessed if C is non-null. SV* sv_setref_pv(SV* rv, const char* classname, PV iv); Copies string into an SV whose reference is C. Set length to 0 to let Perl calculate the string length. SV is blessed if C is non-null. SV* sv_setref_pvn(SV* rv, const char* classname, PV iv, STRLEN length); Tests whether the SV is blessed into the specified class. It does not check inheritance relationships. int sv_isa(SV* sv, const char* name); Tests whether the SV is a reference to a blessed object. int sv_isobject(SV* sv); Tests whether the SV is derived from the specified class. SV can be either a reference to a blessed object or a string containing a class name. This is the function implementing the C functionality. bool sv_derived_from(SV* sv, const char* name); To check if you've got an object derived from a specific class you have to write: if (sv_isobject(sv) && sv_derived_from(sv, class)) { ... } =head2 新しい変数の作成 To create a new Perl variable with an undef value which can be accessed from your Perl script, use the following routines, depending on the variable type. SV* get_sv("package::varname", TRUE); AV* get_av("package::varname", TRUE); HV* get_hv("package::varname", TRUE); Notice the use of TRUE as the second parameter. The new variable can now be set, using the routines appropriate to the data type. There are additional macros whose values may be bitwise OR'ed with the C argument to enable certain extra features. Those bits are: =over =item GV_ADDMULTI Marks the variable as multiply defined, thus preventing the: Name used only once: possible typo warning. =item GV_ADDWARN Issues the warning: Had to create unexpectedly if the variable did not exist before the function was called. =back If you do not specify a package name, the variable is created in the current package. =head2 リファレンスカウンタと揮発属性 Perl uses a reference count-driven garbage collection mechanism. SVs, AVs, or HVs (xV for short in the following) start their life with a reference count of 1. If the reference count of an xV ever drops to 0, then it will be destroyed and its memory made available for reuse. This normally doesn't happen at the Perl level unless a variable is undef'ed or the last variable holding a reference to it is changed or overwritten. At the internal level, however, reference counts can be manipulated with the following macros: int SvREFCNT(SV* sv); SV* SvREFCNT_inc(SV* sv); void SvREFCNT_dec(SV* sv); However, there is one other function which manipulates the reference count of its argument. The C function, you will recall, creates a reference to the specified argument. As a side effect, it increments the argument's reference count. If this is not what you want, use C instead. For example, imagine you want to return a reference from an XSUB function. Inside the XSUB routine, you create an SV which initially has a reference count of one. Then you call C, passing it the just-created SV. This returns the reference as a new SV, but the reference count of the SV you passed to C has been incremented to two. Now you return the reference from the XSUB routine and forget about the SV. But Perl hasn't! Whenever the returned reference is destroyed, the reference count of the original SV is decreased to one and nothing happens. The SV will hang around without any way to access it until Perl itself terminates. This is a memory leak. The correct procedure, then, is to use C instead of C. Then, if and when the last reference is destroyed, the reference count of the SV will go to zero and it will be destroyed, stopping any memory leak. There are some convenience functions available that can help with the destruction of xVs. These functions introduce the concept of "mortality". An xV that is mortal has had its reference count marked to be decremented, but not actually decremented, until "a short time later". Generally the term "short time later" means a single Perl statement, such as a call to an XSUB function. The actual determinant for when mortal xVs have their reference count decremented depends on two macros, SAVETMPS and FREETMPS. See L and L for more details on these macros. "Mortalization" then is at its simplest a deferred C. However, if you mortalize a variable twice, the reference count will later be decremented twice. "Mortal" SVs are mainly used for SVs that are placed on perl's stack. For example an SV which is created just to pass a number to a called sub is made mortal to have it cleaned up automatically when it's popped off the stack. Similarly, results returned by XSUBs (which are pushed on the stack) are often made mortal. To create a mortal variable, use the functions: SV* sv_newmortal() SV* sv_2mortal(SV*) SV* sv_mortalcopy(SV*) The first call creates a mortal SV (with no value), the second converts an existing SV to a mortal SV (and thus defers a call to C), and the third creates a mortal copy of an existing SV. Because C gives the new SV no value,it must normally be given one via C, C, etc. : SV *tmp = sv_newmortal(); sv_setiv(tmp, an_integer); As that is multiple C statements it is quite common so see this idiom instead: SV *tmp = sv_2mortal(newSViv(an_integer)); You should be careful about creating mortal variables. Strange things can happen if you make the same value mortal within multiple contexts, or if you make a variable mortal multiple times. Thinking of "Mortalization" as deferred C should help to minimize such problems. For example if you are passing an SV which you I has high enough REFCNT to survive its use on the stack you need not do any mortalization. If you are not sure then doing an C and C, or making a C is safer. The mortal routines are not just for SVs -- AVs and HVs can be made mortal by passing their address (type-casted to C) to the C or C routines. =head2 スタッシュとグラブ "スタッシュ" とは, パッケージに含まれているすべてのオブジェクトを 格納しているハッシュです. スタッシュの各キーはシンボルの名前です (型が違っても同じ名前なら共有されます). また, ハッシュの各値は GV(グラブ)です. このGVにはその名前の様々なオブジェクトが順番に格納されています. 次のものが(制限されることなく)含まれます. Scalar Value Array Value Hash Value I/O Handle Format Subroutine スカラー値 配列値 ハッシュ値 I/O ハンドル フォーマット 関数 "PL_defstash"と呼ばれる１つのスタッシュがあります. これは "main" パッケージに属する項目を保持しています. ほかのパッケージの項目を取得するためには, パッケージ名に "::" という 文字列を追加してください. C パッケージの項目は PL_defstash の C というスタッシュに 格納されています. C パッケージの項目は C スタッシュの C スタッシュに 格納されています. 特定のパッケージのスタッシュを取得するには次の関数が便利です. HV* gv_stashpv(const char* name, I32 create) HV* gv_stashsv(SV*, I32 create) １つめの関数では文字列リテラルを受け取り, ２つめのものは文字列を格納しているSVを受け取ります. スタッシュはあくまでハッシュなため, 復帰値は C です. Cフラグを設定すると, 新しいパッケージを作成します. C が受け取る名前は, 受け取りたいパッケージの シンボルテーブル名です. デフォルトのパッケージは C
と呼ばれます. ネストしたパッケージに対しては, Perl言語と同じように C<::> で区切られたその名前を C に渡します. 同様に, ブレスされたリファレンスであるSVがあるなら, 次のようにスタッシュポインタを見つけることができます: HV* SvSTASH(SvRV(SV*)); そして次の関数でそのパッケージ名を取得できます: char* HvNAME(HV* stash); オブジェクトをブレス(もしくは再ブレス)するには次の関数を使います: SV* sv_bless(SV*, HV* stash) 最初の引数には, 必ずリファレンスとなっているSV*を渡さなければなりません. ２番目の引数にはスタッシュを渡します. 返されるSV*はほかのSVと同じように扱えます. リファレンスとブレスに関する詳細な情報は, L を参照してください. =head2 ２つのタイプを持つSV Scalar variables normally contain only one type of value, an integer, double, pointer, or reference. Perl will automatically convert the actual scalar data from the stored type into the requested type. Some scalar variables contain more than one type of scalar data. For example, the variable C<$!> contains either the numeric value of C or its string equivalent from either C or C. To force multiple data values into an SV, you must do two things: use the C routines to add the additional scalar type, then set a flag so that Perl will believe it contains more than one type of data. The four macros to set the flags are: SvIOK_on SvNOK_on SvPOK_on SvROK_on The particular macro you must use depends on which C routine you called first. This is because every C routine turns on only the bit for the particular type of data being set, and turns off all the rest. For example, to create a new Perl variable called "dberror" that contains both the numeric and descriptive string error values, you could use the following code: extern int dberror; extern char *dberror_list; SV* sv = get_sv("dberror", TRUE); sv_setiv(sv, (IV) dberror); sv_setpv(sv, dberror_list[dberror]); SvIOK_on(sv); If the order of C and C had been reversed, then the macro C would need to be called instead of C. =head2 マジック変数 [このセクションはまだ準備中です. ここにあるすべての情報は, 使わずに無視してください. 何も書かないでください. 許可されていないことは禁止します. ] どの SV でもマジカルになることがあります, つまり, 普通の SV が持っていない 特殊な機能を持つことができます. これらの機能は SV 構造体の中に C として typedef されている C のリンクリストとして格納されています. struct magic { MAGIC* mg_moremagic; MGVTBL* mg_virtual; U16 mg_private; char mg_type; U8 mg_flags; SV* mg_obj; char* mg_ptr; I32 mg_len; }; これはパッチレベル 0 現在での状態であり, いつでも変わることがあります. =head2 マジックの設定 Perl は sv_magic 関数を使って SV にマジックを追加します: void sv_magic(SV* sv, SV* obj, int how, const char* name, I32 namlen); C 引数は新しいマジック機能を加える SV へのポインタです. C がまだマジカルではなければ, Perl は C を C 型へと変換するために C マクロを 使います. Perl はそれからマジック機能のリンクリストの 先頭への新しいマジックの追加を続けます. 先に設定されていた同じタイプのマジックのエントリは 削除されます. これはオーバーライドでき, 同じタイプのマジックの複数のインスタンスを1つのSVに 関連づけることもできる点に注意してください. C 及び C 引数はマジックに文字列を 関連づけるために使われ, 通常は変数の名前です. C は C フィールドに格納され, C が0より大きいか若しくは0と等しいかに応じて C がnullでなければ C による C のコピー若しくは C そのものが C フィールドに格納されます. 特別なケースとして, C<(name && namlen == HEf_SVKEY)> の時は C には C が設定されていて, その REFCNT を増加させてそのまま格納されます. The sv_magic function uses C to determine which, if any, predefined "Magic Virtual Table" should be assigned to the C field. See the L section below. The C argument is also stored in the C field. The value of C should be chosen from the set of macros C found in F. Note that before these macros were added, Perl internals used to directly use character literals, so you may occasionally come across old code or documentation referring to 'U' magic rather than C for example. The C argument is stored in the C field of the C structure. If it is not the same as the C argument, the reference count of the C object is incremented. If it is the same, or if the C argument is C, or if it is a NULL pointer, then C is merely stored, without the reference count being incremented. See also C in L for a more flexible way to add magic to an SV. There is also a function to add magic to an C: void hv_magic(HV *hv, GV *gv, int how); This simply calls C and coerces the C argument into an C. To remove the magic from an SV, call the function sv_unmagic: void sv_unmagic(SV *sv, int type); The C argument should be equal to the C value when the C was initially made magical. =head2 マジック仮想テーブル The C field in the C structure is a pointer to an C, which is a structure of function pointers and stands for "Magic Virtual Table" to handle the various operations that might be applied to that variable. The C has five pointers to the following routine types: int (*svt_get)(SV* sv, MAGIC* mg); int (*svt_set)(SV* sv, MAGIC* mg); U32 (*svt_len)(SV* sv, MAGIC* mg); int (*svt_clear)(SV* sv, MAGIC* mg); int (*svt_free)(SV* sv, MAGIC* mg); This MGVTBL structure is set at compile-time in F and there are currently 19 types (or 21 with overloading turned on). These different structures contain pointers to various routines that perform additional actions depending on which function is being called. Function pointer Action taken ---------------- ------------ svt_get Do something before the value of the SV is retrieved. svt_set Do something after the SV is assigned a value. svt_len Report on the SV's length. svt_clear Clear something the SV represents. svt_free Free any extra storage associated with the SV. For instance, the MGVTBL structure called C (which corresponds to an C of C) contains: { magic_get, magic_set, magic_len, 0, 0 } Thus, when an SV is determined to be magical and of type C, if a get operation is being performed, the routine C is called. All the various routines for the various magical types begin with C. NOTE: the magic routines are not considered part of the Perl API, and may not be exported by the Perl library. The current kinds of Magic Virtual Tables are: mg_type (old-style char and macro) MGVTBL Type of magic -------------------------- ------ ---------------------------- \0 PERL_MAGIC_sv vtbl_sv Special scalar variable A PERL_MAGIC_overload vtbl_amagic %OVERLOAD hash a PERL_MAGIC_overload_elem vtbl_amagicelem %OVERLOAD hash element c PERL_MAGIC_overload_table (none) Holds overload table (AMT) on stash B PERL_MAGIC_bm vtbl_bm Boyer-Moore (fast string search) D PERL_MAGIC_regdata vtbl_regdata Regex match position data (@+ and @- vars) d PERL_MAGIC_regdatum vtbl_regdatum Regex match position data element E PERL_MAGIC_env vtbl_env %ENV hash e PERL_MAGIC_envelem vtbl_envelem %ENV hash element f PERL_MAGIC_fm vtbl_fm Formline ('compiled' format) g PERL_MAGIC_regex_global vtbl_mglob m//g target / study()ed string I PERL_MAGIC_isa vtbl_isa @ISA array i PERL_MAGIC_isaelem vtbl_isaelem @ISA array element k PERL_MAGIC_nkeys vtbl_nkeys scalar(keys()) lvalue L PERL_MAGIC_dbfile (none) Debugger %_ and C magic types are defined specifically for use by extensions and will not be used by perl itself. Extensions can use C magic to 'attach' private information to variables (typically objects). This is especially useful because there is no way for normal perl code to corrupt this private information (unlike using extra elements of a hash object). Similarly, C magic can be used much like tie() to call a C function any time a scalar's value is used or changed. The C's C field points to a C structure: struct ufuncs { I32 (*uf_val)(pTHX_ IV, SV*); I32 (*uf_set)(pTHX_ IV, SV*); IV uf_index; }; When the SV is read from or written to, the C or C function will be called with C as the first arg and a pointer to the SV as the second. A simple example of how to add C magic is shown below. Note that the ufuncs structure is copied by sv_magic, so you can safely allocate it on the stack. void Umagic(sv) SV *sv; PREINIT: struct ufuncs uf; CODE: uf.uf_val = &my_get_fn; uf.uf_set = &my_set_fn; uf.uf_index = 0; sv_magic(sv, 0, PERL_MAGIC_uvar, (char*)&uf, sizeof(uf)); Note that because multiple extensions may be using C or C magic, it is important for extensions to take extra care to avoid conflict. Typically only using the magic on objects blessed into the same class as the extension is sufficient. For C magic, it may also be appropriate to add an I32 'signature' at the top of the private data area and check that. Also note that the C and C functions described earlier do B invoke 'set' magic on their targets. This must be done by the user either by calling the C macro after calling these functions, or by using one of the C or C functions. Similarly, generic C code must call the C macro to invoke any 'get' magic if they use an SV obtained from external sources in functions that don't handle magic. See L for a description of these functions. For example, calls to the C functions typically need to be followed by C, but they don't need a prior C since their implementation handles 'get' magic. =head2 マジックの検索 MAGIC* mg_find(SV*, int type); /* Finds the magic pointer of that type */ このルーティンはSVに格納されているMIAGIC構造体へのポインタを返します. SVがmagicの機能を持っていなければNULLが返されます. またSVがSVt_PVMGでないときには, Perl はおそらくコアダンプするでしょう. int mg_copy(SV* sv, SV* nsv, const char* key, STRLEN klen); このルーティンはsvがどの種類のmagicを持っているのか見るために使われます. もし mg_type フィールドが大文字だったらなら mg_obj は nsv にコピーされますが mg_typeフィールドは小文字になります. =head2 tie されたハッシュと配列のマジックの理解 Tied hashes and arrays are magical beasts of the C magic type. WARNING: As of the 5.004 release, proper usage of the array and hash access functions requires understanding a few caveats. Some of these caveats are actually considered bugs in the API, to be fixed in later releases, and are bracketed with [MAYCHANGE] below. If you find yourself actually applying such information in this section, be aware that the behavior may change in the future, umm, without warning. The perl tie function associates a variable with an object that implements the various GET, SET, etc methods. To perform the equivalent of the perl tie function from an XSUB, you must mimic this behaviour. The code below carries out the necessary steps - firstly it creates a new hash, and then creates a second hash which it blesses into the class which will implement the tie methods. Lastly it ties the two hashes together, and returns a reference to the new tied hash. Note that the code below does NOT call the TIEHASH method in the MyTie class - see L for details on how to do this. SV* mytie() PREINIT: HV *hash; HV *stash; SV *tie; CODE: hash = newHV(); tie = newRV_noinc((SV*)newHV()); stash = gv_stashpv("MyTie", TRUE); sv_bless(tie, stash); hv_magic(hash, (GV*)tie, PERL_MAGIC_tied); RETVAL = newRV_noinc(hash); OUTPUT: RETVAL The C function, when given a tied array argument, merely copies the magic of the array onto the value to be "stored", using C. It may also return NULL, indicating that the value did not actually need to be stored in the array. [MAYCHANGE] After a call to C on a tied array, the caller will usually need to call C to actually invoke the perl level "STORE" method on the TIEARRAY object. If C did return NULL, a call to C will also be usually necessary to avoid a memory leak. [/MAYCHANGE] The previous paragraph is applicable verbatim to tied hash access using the C and C functions as well. C and the corresponding hash functions C and C actually return an undefined mortal value whose magic has been initialized using C. Note the value so returned does not need to be deallocated, as it is already mortal. [MAYCHANGE] But you will need to call C on the returned value in order to actually invoke the perl level "FETCH" method on the underlying TIE object. Similarly, you may also call C on the return value after possibly assigning a suitable value to it using C, which will invoke the "STORE" method on the TIE object. [/MAYCHANGE] [MAYCHANGE] In other words, the array or hash fetch/store functions don't really fetch and store actual values in the case of tied arrays and hashes. They merely call C to attach magic to the values that were meant to be "stored" or "fetched". Later calls to C and C actually do the job of invoking the TIE methods on the underlying objects. Thus the magic mechanism currently implements a kind of lazy access to arrays and hashes. Currently (as of perl version 5.004), use of the hash and array access functions requires the user to be aware of whether they are operating on "normal" hashes and arrays, or on their tied variants. The API may be changed to provide more transparent access to both tied and normal data types in future versions. [/MAYCHANGE] You would do well to understand that the TIEARRAY and TIEHASH interfaces are mere sugar to invoke some perl method calls while using the uniform hash and array syntax. The use of this sugar imposes some overhead (typically about two to four extra opcodes per FETCH/STORE operation, in addition to the creation of all the mortal variables required to invoke the methods). This overhead will be comparatively small if the TIE methods are themselves substantial, but if they are only a few statements long, the overhead will not be insignificant. =head2 変更の局所化 Perl has a very handy construction { local $var = 2; ... } This construction is I equivalent to { my $oldvar = $var; $var = 2; ... $var = $oldvar; } The biggest difference is that the first construction would reinstate the initial value of $var, irrespective of how control exits the block: C, C, C/C, etc. It is a little bit more efficient as well. There is a way to achieve a similar task from C via Perl API: create a I, and arrange for some changes to be automatically undone at the end of it, either explicit, or via a non-local exit (via die()). A I-like construct is created by a pair of C/C macros (see L). Such a construct may be created specially for some important localized task, or an existing one (like boundaries of enclosing Perl subroutine/block, or an existing pair for freeing TMPs) may be used. (In the second case the overhead of additional localization must be almost negligible.) Note that any XSUB is automatically enclosed in an C/C pair. Inside such a I the following service is available: =over 4 =item C =item C =item C =item C These macros arrange things to restore the value of integer variable C at the end of enclosing I. =item C =item C These macros arrange things to restore the value of pointers C and C

. C must be a pointer of a type which survives conversion to C and back, C

should be able to survive conversion to C and back. =item C The refcount of C would be decremented at the end of I. This is similar to C in that it is also a mechanism for doing a delayed C. However, while C extends the lifetime of C until the beginning of the next statement, C extends it until the end of the enclosing scope. These lifetimes can be wildly different. Also compare C. =item C Just like C, but mortalizes C at the end of the current scope instead of decrementing its reference count. This usually has the effect of keeping C alive until the statement that called the currently live scope has finished executing. =item C The C is op_free()ed at the end of I. =item C The chunk of memory which is pointed to by C

is Safefree()ed at the end of I. =item C Clears a slot in the current scratchpad which corresponds to C at the end of I. =item C The key C of C is deleted at the end of I. The string pointed to by C is Safefree()ed. If one has a I in short-lived storage, the corresponding string may be reallocated like this: SAVEDELETE(PL_defstash, savepv(tmpbuf), strlen(tmpbuf)); =item C At the end of I the function C is called with the only argument C

. =item C At the end of I the function C is called with the implicit context argument (if any), and C

. =item C The current offset on the Perl internal stack (cf. C) is restored at the end of I. =back The following API list contains functions, thus one needs to provide pointers to the modifiable data explicitly (either C pointers, or Perlish Cs). Where the above macros take C, a similar function takes C. =over 4 =item C Equivalent to Perl code C. =item C =item C Similar to C, but localize C<@gv> and C<%gv>. =item C Duplicates the current value of C, on the exit from the current C/C I will restore the value of C using the stored value. =item C A variant of C which takes multiple arguments via an array C of C of length C. =item C Similar to C, but will reinstate an C. =item C =item C Similar to C, but localize C and C. =back The C module implements localization of the basic types within the I. People who are interested in how to localize things in the containing scope should take a look there too. =head1 サブルーチン =head2 XSUB と引数スタック The XSUB mechanism is a simple way for Perl programs to access C subroutines. An XSUB routine will have a stack that contains the arguments from the Perl program, and a way to map from the Perl data structures to a C equivalent. The stack arguments are accessible through the C macro, which returns the C'th stack argument. Argument 0 is the first argument passed in the Perl subroutine call. These arguments are C, and can be used anywhere an C is used. Most of the time, output from the C routine can be handled through use of the RETVAL and OUTPUT directives. However, there are some cases where the argument stack is not already long enough to handle all the return values. An example is the POSIX tzname() call, which takes no arguments, but returns two, the local time zone's standard and summer time abbreviations. To handle this situation, the PPCODE directive is used and the stack is extended using the macro: EXTEND(SP, num); where C is the macro that represents the local copy of the stack pointer, and C is the number of elements the stack should be extended by. Now that there is room on the stack, values can be pushed on it using C macro. The pushed values will often need to be "mortal" (See L): PUSHs(sv_2mortal(newSViv(an_integer))) PUSHs(sv_2mortal(newSVuv(an_unsigned_integer))) PUSHs(sv_2mortal(newSVnv(a_double))) PUSHs(sv_2mortal(newSVpv("Some String",0))) And now the Perl program calling C, the two values will be assigned as in: ($standard_abbrev, $summer_abbrev) = POSIX::tzname; An alternate (and possibly simpler) method to pushing values on the stack is to use the macro: XPUSHs(SV*) This macro automatically adjust the stack for you, if needed. Thus, you do not need to call C to extend the stack. Despite their suggestions in earlier versions of this document the macros C<(X)PUSH[iunp]> are I suited to XSUBs which return multiple results. For that, either stick to the C<(X)PUSHs> macros shown above, or use the new C macros instead; see L. For more information, consult L and L. =head2 C プラグラムからの Perl ルーチンの呼び出し There are four routines that can be used to call a Perl subroutine from within a C program. These four are: I32 call_sv(SV*, I32); I32 call_pv(const char*, I32); I32 call_method(const char*, I32); I32 call_argv(const char*, I32, register char**); The routine most often used is C. The C argument contains either the name of the Perl subroutine to be called, or a reference to the subroutine. The second argument consists of flags that control the context in which the subroutine is called, whether or not the subroutine is being passed arguments, how errors should be trapped, and how to treat return values. All four routines return the number of arguments that the subroutine returned on the Perl stack. These routines used to be called C, etc., before Perl v5.6.0, but those names are now deprecated; macros of the same name are provided for compatibility. When using any of these routines (except C), the programmer must manipulate the Perl stack. These include the following macros and functions: dSP SP PUSHMARK() PUTBACK SPAGAIN ENTER SAVETMPS FREETMPS LEAVE XPUSH*() POP*() For a detailed description of calling conventions from C to Perl, consult L. =head2 メモリの確保 =head3 確保 All memory meant to be used with the Perl API functions should be manipulated using the macros described in this section. The macros provide the necessary transparency between differences in the actual malloc implementation that is used within perl. It is suggested that you enable the version of malloc that is distributed with Perl. It keeps pools of various sizes of unallocated memory in order to satisfy allocation requests more quickly. However, on some platforms, it may cause spurious malloc or free errors. The following three macros are used to initially allocate memory : Newx(pointer, number, type); Newxc(pointer, number, type, cast); Newxz(pointer, number, type); The first argument C should be the name of a variable that will point to the newly allocated memory. The second and third arguments C and C specify how many of the specified type of data structure should be allocated. The argument C is passed to C. The final argument to C, C, should be used if the C argument is different from the C argument. Unlike the C and C macros, the C macro calls C to zero out all the newly allocated memory. =head3 再確保 Renew(pointer, number, type); Renewc(pointer, number, type, cast); Safefree(pointer) These three macros are used to change a memory buffer size or to free a piece of memory no longer needed. The arguments to C and C match those of C and C with the exception of not needing the "magic cookie" argument. =head3 移動 Move(source, dest, number, type); Copy(source, dest, number, type); Zero(dest, number, type); These three macros are used to move, copy, or zero out previously allocated memory. The C and C arguments point to the source and destination starting points. Perl will move, copy, or zero out C instances of the size of the C data structure (using the C function). =head2 PerlIO The most recent development releases of Perl has been experimenting with removing Perl's dependency on the "normal" standard I/O suite and allowing other stdio implementations to be used. This involves creating a new abstraction layer that then calls whichever implementation of stdio Perl was compiled with. All XSUBs should now use the functions in the PerlIO abstraction layer and not make any assumptions about what kind of stdio is being used. For a complete description of the PerlIO abstraction, consult L. =head2 C の値を Perl スタックに置く A lot of opcodes (this is an elementary operation in the internal perl stack machine) put an SV* on the stack. However, as an optimization the corresponding SV is (usually) not recreated each time. The opcodes reuse specially assigned SVs (Is) which are (as a corollary) not constantly freed/created. Each of the targets is created only once (but see L below), and when an opcode needs to put an integer, a double, or a string on stack, it just sets the corresponding parts of its I and puts the I on stack. The macro to put this target on stack is C, and it is directly used in some opcodes, as well as indirectly in zillions of others, which use it via C<(X)PUSH[iunp]>. Because the target is reused, you must be careful when pushing multiple values on the stack. The following code will not do what you think: XPUSHi(10); XPUSHi(20); This translates as "set C to 10, push a pointer to C onto the stack; set C to 20, push a pointer to C onto the stack". At the end of the operation, the stack does not contain the values 10 and 20, but actually contains two pointers to C, which we have set to 20. If you need to push multiple different values then you should either use the C<(X)PUSHs> macros, or else use the new C macros, none of which make use of C. The C<(X)PUSHs> macros simply push an SV* on the stack, which, as noted under L, will often need to be "mortal". The new C macros make this a little easier to achieve by creating a new mortal for you (via C<(X)PUSHmortal>), pushing that onto the stack (extending it if necessary in the case of the C macros), and then setting its value. Thus, instead of writing this to "fix" the example above: XPUSHs(sv_2mortal(newSViv(10))) XPUSHs(sv_2mortal(newSViv(20))) you can simply write: mXPUSHi(10) mXPUSHi(20) On a related note, if you do use C<(X)PUSH[iunp]>, then you're going to need a C in your variable declarations so that the C<*PUSH*> macros can make use of the local variable C. See also C and C. =head2 スクラッチパッド The question remains on when the SVs which are Is for opcodes are created. The answer is that they are created when the current unit -- a subroutine or a file (for opcodes for statements outside of subroutines) -- is compiled. During this time a special anonymous Perl array is created, which is called a scratchpad for the current unit. A scratchpad keeps SVs which are lexicals for the current unit and are targets for opcodes. One can deduce that an SV lives on a scratchpad by looking on its flags: lexicals have C set, and Is have C set. The correspondence between OPs and Is is not 1-to-1. Different OPs in the compile tree of the unit can use the same target, if this would not conflict with the expected life of the temporary. =head2 スクラッチパッドと再帰 In fact it is not 100% true that a compiled unit contains a pointer to the scratchpad AV. In fact it contains a pointer to an AV of (initially) one element, and this element is the scratchpad AV. Why do we need an extra level of indirection? The answer is B, and maybe B. Both these can create several execution pointers going into the same subroutine. For the subroutine-child not write over the temporaries for the subroutine-parent (lifespan of which covers the call to the child), the parent and the child should have different scratchpads. (I the lexicals should be separate anyway!) So each subroutine is born with an array of scratchpads (of length 1). On each entry to the subroutine it is checked that the current depth of the recursion is not more than the length of this array, and if it is, new scratchpad is created and pushed into the array. The Is on this scratchpad are Cs, but they are already marked with correct flags. =head1 コンパイルコード =head2 コードツリー Here we describe the internal form your code is converted to by Perl. Start with a simple example: $a = $b + $c; This is converted to a tree similar to this one: assign-to / \ + $a / \ $b $c (but slightly more complicated). This tree reflects the way Perl parsed your code, but has nothing to do with the execution order. There is an additional "thread" going through the nodes of the tree which shows the order of execution of the nodes. In our simplified example above it looks like: $b ---> $c ---> + ---> $a ---> assign-to But with the actual compile tree for C<$a = $b + $c> it is different: some nodes I. As a corollary, though the actual tree contains more nodes than our simplified example, the execution order is the same as in our example. =head2 ツリーの調査 If you have your perl compiled for debugging (usually done with C<-DDEBUGGING> on the C command line), you may examine the compiled tree by specifying C<-Dx> on the Perl command line. The output takes several lines per node, and for C<$b+$c> it looks like this: 5 TYPE = add ===> 6 TARG = 1 FLAGS = (SCALAR,KIDS) { TYPE = null ===> (4) (was rv2sv) FLAGS = (SCALAR,KIDS) { 3 TYPE = gvsv ===> 4 FLAGS = (SCALAR) GV = main::b } } { TYPE = null ===> (5) (was rv2sv) FLAGS = (SCALAR,KIDS) { 4 TYPE = gvsv ===> 5 FLAGS = (SCALAR) GV = main::c } } This tree has 5 nodes (one per C specifier), only 3 of them are not optimized away (one per number in the left column). The immediate children of the given node correspond to C<{}> pairs on the same level of indentation, thus this listing corresponds to the tree: add / \ null null | | gvsv gvsv The execution order is indicated by C<===E> marks, thus it is C<3 4 5 6> (node C<6> is not included into above listing), i.e., C. Each of these nodes represents an op, a fundamental operation inside the Perl core. The code which implements each operation can be found in the F files; the function which implements the op with type C is C, and so on. As the tree above shows, different ops have different numbers of children: C is a binary operator, as one would expect, and so has two children. To accommodate the various different numbers of children, there are various types of op data structure, and they link together in different ways. The simplest type of op structure is C: this has no children. Unary operators, Cs, have one child, and this is pointed to by the C field. Binary operators (Cs) have not only an C field but also an C field. The most complex type of op is a C, which has any number of children. In this case, the first child is pointed to by C and the last child by C. The children in between can be found by iteratively following the C pointer from the first child to the last. There are also two other op types: a C holds a regular expression, and has no children, and a C may or may not have children. If the C field is non-zero, it behaves like a C. To complicate matters, if a C is actually a C op after optimization (see L) it will still have children in accordance with its former type. Another way to examine the tree is to use a compiler back-end module, such as L. =head2 コンパイルパス 1: ルーチンのチェック The tree is created by the compiler while I code feeds it the constructions it recognizes. Since I works bottom-up, so does the first pass of perl compilation. What makes this pass interesting for perl developers is that some optimization may be performed on this pass. This is optimization by so-called "check routines". The correspondence between node names and corresponding check routines is described in F (do not forget to run C if you modify this file). A check routine is called when the node is fully constructed except for the execution-order thread. Since at this time there are no back-links to the currently constructed node, one can do most any operation to the top-level node, including freeing it and/or creating new nodes above/below it. The check routine returns the node which should be inserted into the tree (if the top-level node was not modified, check routine returns its argument). By convention, check routines have names C. They are usually called from C subroutines (or C) (which in turn are called from F). =head2 コンパイルパス 1a: 定数のたたみ込み Immediately after the check routine is called the returned node is checked for being compile-time executable. If it is (the value is judged to be constant) it is immediately executed, and a I node with the "return value" of the corresponding subtree is substituted instead. The subtree is deleted. If constant folding was not performed, the execution-order thread is created. =head2 コンパイルパス 2: コンテキストの伝播 When a context for a part of compile tree is known, it is propagated down through the tree. At this time the context can have 5 values (instead of 2 for runtime context): void, boolean, scalar, list, and lvalue. In contrast with the pass 1 this pass is processed from top to bottom: a node's context determines the context for its children. Additional context-dependent optimizations are performed at this time. Since at this moment the compile tree contains back-references (via "thread" pointers), nodes cannot be free()d now. To allow optimized-away nodes at this stage, such nodes are null()ified instead of free()ing (i.e. their type is changed to OP_NULL). =head2 コンパイルパス 3: 局所的な最適化 After the compile tree for a subroutine (or for an C or a file) is created, an additional pass over the code is performed. This pass is neither top-down or bottom-up, but in the execution order (with additional complications for conditionals). These optimizations are done in the subroutine peep(). Optimizations performed at this stage are subject to the same restrictions as in the pass 2. =head2 変更可能な op 実行 The compile tree is executed in a runops function. There are two runops functions, in F and in F. C is used with DEBUGGING and C is used otherwise. For fine control over the execution of the compile tree it is possible to provide your own runops function. It's probably best to copy one of the existing runops functions and change it to suit your needs. Then, in the BOOT section of your XS file, add the line: PL_runops = my_runops; This function should be as efficient as possible to keep your programs running as fast as possible. =head1 内部データ構造を C 関数で調査する To aid debugging, the source file F contains a number of functions which produce formatted output of internal data structures. The most commonly used of these functions is C; it's used for dumping SVs, AVs, HVs, and CVs. The C module calls C to produce debugging output from Perl-space, so users of that module should already be familiar with its format. C can be used to dump an C structure or any of its derivatives, and produces output similar to C; in fact, C will dump the main root of the code being evaluated, exactly like C<-Dx>. Other useful functions are C, which turns a C into an op tree, C which calls C on all the subroutines in a package like so: (Thankfully, these are all xsubs, so there is no op tree) (gdb) print Perl_dump_packsubs(PL_defstash) SUB attributes::bootstrap = (xsub 0x811fedc 0) SUB UNIVERSAL::can = (xsub 0x811f50c 0) SUB UNIVERSAL::isa = (xsub 0x811f304 0) SUB UNIVERSAL::VERSION = (xsub 0x811f7ac 0) SUB DynaLoader::boot_DynaLoader = (xsub 0x805b188 0) and C, which dumps all the subroutines in the stash and the op tree of the main root. =head1 複数の処理系と並列処理がどのようにサポートされているか =head2 背景と PERL_IMPLICIT_CONTEXT The Perl interpreter can be regarded as a closed box: it has an API for feeding it code or otherwise making it do things, but it also has functions for its own use. This smells a lot like an object, and there are ways for you to build Perl so that you can have multiple interpreters, with one interpreter represented either as a C structure, or inside a thread-specific structure. These structures contain all the context, the state of that interpreter. Two macros control the major Perl build flavors: MULTIPLICITY and USE_5005THREADS. The MULTIPLICITY build has a C structure that packages all the interpreter state, and there is a similar thread-specific data structure under USE_5005THREADS. In both cases, PERL_IMPLICIT_CONTEXT is also normally defined, and enables the support for passing in a "hidden" first argument that represents all three data structures. All this obviously requires a way for the Perl internal functions to be either subroutines taking some kind of structure as the first argument, or subroutines taking nothing as the first argument. To enable these two very different ways of building the interpreter, the Perl source (as it does in so many other situations) makes heavy use of macros and subroutine naming conventions. First problem: deciding which functions will be public API functions and which will be private. All functions whose names begin C are private (think "S" for "secret" or "static"). All other functions begin with "Perl_", but just because a function begins with "Perl_" does not mean it is part of the API. (See L.) The easiest way to be B a function is part of the API is to find its entry in L. If it exists in L, it's part of the API. If it doesn't, and you think it should be (i.e., you need it for your extension), send mail via L explaining why you think it should be. Second problem: there must be a syntax so that the same subroutine declarations and calls can pass a structure as their first argument, or pass nothing. To solve this, the subroutines are named and declared in a particular way. Here's a typical start of a static function used within the Perl guts: STATIC void S_incline(pTHX_ char *s) STATIC becomes "static" in C, and may be #define'd to nothing in some configurations in future. A public function (i.e. part of the internal API, but not necessarily sanctioned for use in extensions) begins like this: void Perl_sv_setiv(pTHX_ SV* dsv, IV num) C is one of a number of macros (in perl.h) that hide the details of the interpreter's context. THX stands for "thread", "this", or "thingy", as the case may be. (And no, George Lucas is not involved. :-) The first character could be 'p' for a B

rototype, 'a' for Brgument, or 'd' for Beclaration, so we have C, C and C, and their variants. When Perl is built without options that set PERL_IMPLICIT_CONTEXT, there is no first argument containing the interpreter's context. The trailing underscore in the pTHX_ macro indicates that the macro expansion needs a comma after the context argument because other arguments follow it. If PERL_IMPLICIT_CONTEXT is not defined, pTHX_ will be ignored, and the subroutine is not prototyped to take the extra argument. The form of the macro without the trailing underscore is used when there are no additional explicit arguments. When a core function calls another, it must pass the context. This is normally hidden via macros. Consider C. It expands into something like this: #ifdef PERL_IMPLICIT_CONTEXT #define sv_setiv(a,b) Perl_sv_setiv(aTHX_ a, b) /* can't do this for vararg functions, see below */ #else #define sv_setiv Perl_sv_setiv #endif This works well, and means that XS authors can gleefully write: sv_setiv(foo, bar); and still have it work under all the modes Perl could have been compiled with. This doesn't work so cleanly for varargs functions, though, as macros imply that the number of arguments is known in advance. Instead we either need to spell them out fully, passing C as the first argument (the Perl core tends to do this with functions like Perl_warner), or use a context-free version. The context-free version of Perl_warner is called Perl_warner_nocontext, and does not take the extra argument. Instead it does dTHX; to get the context from thread-local storage. We C<#define warner Perl_warner_nocontext> so that extensions get source compatibility at the expense of performance. (Passing an arg is cheaper than grabbing it from thread-local storage.) You can ignore [pad]THXx when browsing the Perl headers/sources. Those are strictly for use within the core. Extensions and embedders need only be aware of [pad]THX. =head2 dTHR に何が起こっているのか C was introduced in perl 5.005 to support the older thread model. The older thread model now uses the C mechanism to pass context pointers around, so C is not useful any more. Perl 5.6.0 and later still have it for backward source compatibility, but it is defined to be a no-op. =head2 どのようにしてこの全てを拡張で使うのか When Perl is built with PERL_IMPLICIT_CONTEXT, extensions that call any functions in the Perl API will need to pass the initial context argument somehow. The kicker is that you will need to write it in such a way that the extension still compiles when Perl hasn't been built with PERL_IMPLICIT_CONTEXT enabled. There are three ways to do this. First, the easy but inefficient way, which is also the default, in order to maintain source compatibility with extensions: whenever XSUB.h is #included, it redefines the aTHX and aTHX_ macros to call a function that will return the context. Thus, something like: sv_setiv(sv, num); in your extension will translate to this when PERL_IMPLICIT_CONTEXT is in effect: Perl_sv_setiv(Perl_get_context(), sv, num); or to this otherwise: Perl_sv_setiv(sv, num); You have to do nothing new in your extension to get this; since the Perl library provides Perl_get_context(), it will all just work. The second, more efficient way is to use the following template for your Foo.xs: #define PERL_NO_GET_CONTEXT /* we want efficiency */ #include "EXTERN.h" #include "perl.h" #include "XSUB.h" static my_private_function(int arg1, int arg2); static SV * my_private_function(int arg1, int arg2) { dTHX; /* fetch context */ ... call many Perl API functions ... } [... etc ...] MODULE = Foo PACKAGE = Foo /* typical XSUB */ void my_xsub(arg) int arg CODE: my_private_function(arg, 10); Note that the only two changes from the normal way of writing an extension is the addition of a C<#define PERL_NO_GET_CONTEXT> before including the Perl headers, followed by a C declaration at the start of every function that will call the Perl API. (You'll know which functions need this, because the C compiler will complain that there's an undeclared identifier in those functions.) No changes are needed for the XSUBs themselves, because the XS() macro is correctly defined to pass in the implicit context if needed. The third, even more efficient way is to ape how it is done within the Perl guts: #define PERL_NO_GET_CONTEXT /* we want efficiency */ #include "EXTERN.h" #include "perl.h" #include "XSUB.h" /* pTHX_ only needed for functions that call Perl API */ static my_private_function(pTHX_ int arg1, int arg2); static SV * my_private_function(pTHX_ int arg1, int arg2) { /* dTHX; not needed here, because THX is an argument */ ... call Perl API functions ... } [... etc ...] MODULE = Foo PACKAGE = Foo /* typical XSUB */ void my_xsub(arg) int arg CODE: my_private_function(aTHX_ arg, 10); This implementation never has to fetch the context using a function call, since it is always passed as an extra argument. Depending on your needs for simplicity or efficiency, you may mix the previous two approaches freely. Never add a comma after C yourself--always use the form of the macro with the underscore for functions that take explicit arguments, or the form without the argument for functions with no explicit arguments. =head2 複数のスレッドから perl を呼び出すときに何か特別なことをするべきか If you create interpreters in one thread and then proceed to call them in another, you need to make sure perl's own Thread Local Storage (TLS) slot is initialized correctly in each of those threads. The C and C API functions will automatically set the TLS slot to the interpreter they created, so that there is no need to do anything special if the interpreter is always accessed in the same thread that created it, and that thread did not create or call any other interpreters afterwards. If that is not the case, you have to set the TLS slot of the thread before calling any functions in the Perl API on that particular interpreter. This is done by calling the C macro in that thread as the first thing you do: /* do this before doing anything else with some_perl */ PERL_SET_CONTEXT(some_perl); ... other Perl API calls on some_perl go here ... =head2 今後の予定と PERL_IMPLICIT_SYS Just as PERL_IMPLICIT_CONTEXT provides a way to bundle up everything that the interpreter knows about itself and pass it around, so too are there plans to allow the interpreter to bundle up everything it knows about the environment it's running on. This is enabled with the PERL_IMPLICIT_SYS macro. Currently it only works with USE_ITHREADS and USE_5005THREADS on Windows (see inside iperlsys.h). This allows the ability to provide an extra pointer (called the "host" environment) for all the system calls. This makes it possible for all the system stuff to maintain their own state, broken down into seven C structures. These are thin wrappers around the usual system calls (see win32/perllib.c) for the default perl executable, but for a more ambitious host (like the one that would do fork() emulation) all the extra work needed to pretend that different interpreters are actually different "processes", would be done here. The Perl engine/interpreter and the host are orthogonal entities. There could be one or more interpreters in a process, and one or more "hosts", with free association between them. =head1 内部関数 All of Perl's internal functions which will be exposed to the outside world are prefixed by C so that they will not conflict with XS functions or functions used in a program in which Perl is embedded. Similarly, all global variables begin with C. (By convention, static functions start with C.) Inside the Perl core, you can get at the functions either with or without the C prefix, thanks to a bunch of defines that live in F. This header file is generated automatically from F and F. F also creates the prototyping header files for the internal functions, generates the documentation and a lot of other bits and pieces. It's important that when you add a new function to the core or change an existing one, you change the data in the table in F as well. Here's a sample entry from that table: Apd |SV** |av_fetch |AV* ar|I32 key|I32 lval The second column is the return type, the third column the name. Columns after that are the arguments. The first column is a set of flags: =over 3 =item A This function is a part of the public API. All such functions should also have 'd', very few do not. =item p This function has a C prefix; i.e. it is defined as C. =item d This function has documentation using the C feature which we'll look at in a second. Some functions have 'd' but not 'A'; docs are good. =back Other available flags are: =over 3 =item s This is a static function and is defined as C, and usually called within the sources as C. =item n This does not need a interpreter context, so the definition has no C, and it follows that callers don't use C. (See L.) =item r This function never returns; C, C and friends. =item f This function takes a variable number of arguments, C style. The argument list should end with C<...>, like this: Afprd |void |croak |const char* pat|... =item M This function is part of the experimental development API, and may change or disappear without notice. =item o This function should not have a compatibility macro to define, say, C to C. It must be called as C. =item x This function isn't exported out of the Perl core. =item m This is implemented as a macro. =item X This function is explicitly exported. =item E This function is visible to extensions included in the Perl core. =item b Binary backward compatibility; this function is a macro but also has a C implementation (which is exported). =item others See the comments at the top of C for others. =back If you edit F or F, you will need to run C to force a rebuild of F and other auto-generated files. =head2 IV, UV, NV の整形出力 If you are printing IVs, UVs, or NVS instead of the stdio(3) style formatting codes like C<%d>, C<%ld>, C<%f>, you should use the following macros for portability IVdf IV in decimal UVuf UV in decimal UVof UV in octal UVxf UV in hexadecimal NVef NV %e-like NVff NV %f-like NVgf NV %g-like These will take care of 64-bit integers and long doubles. For example: printf("IV is %"IVdf"\n", iv); The IVdf will expand to whatever is the correct format for the IVs. If you are printing addresses of pointers, use UVxf combined with PTR2UV(), do not use %lx or %p. =head2 ポインタから整数にと整数からポインタに Because pointer size does not necessarily equal integer size, use the follow macros to do it right. PTR2UV(pointer) PTR2IV(pointer) PTR2NV(pointer) INT2PTR(pointertotype, integer) For example: IV iv = ...; SV *sv = INT2PTR(SV*, iv); and AV *av = ...; UV uv = PTR2UV(av); =head2 ソース中のドキュメント There's an effort going on to document the internal functions and automatically produce reference manuals from them - L is one such manual which details all the functions which are available to XS writers. L is the autogenerated manual for the functions which are not part of the API and are supposedly for internal use only. Source documentation is created by putting POD comments into the C source, like this: /* =for apidoc sv_setiv Copies an integer into the given SV. Does not handle 'set' magic. See C. =cut */ Please try and supply some documentation if you add functions to the Perl core. =head2 下位互換性 The Perl API changes over time. New functions are added or the interfaces of existing functions are changed. The C module tries to provide compatibility code for some of these changes, so XS writers don't have to code it themselves when supporting multiple versions of Perl. C generates a C header file F that can also be run as a Perl script. To generate F, run: perl -MDevel::PPPort -eDevel::PPPort::WriteFile Besides checking existing XS code, the script can also be used to retrieve compatibility information for various API calls using the C<--api-info> command line switch. For example: % perl ppport.h --api-info=sv_magicext For details, see C. =head1 ユニコードサポート Perl 5.6.0 introduced Unicode support. It's important for porters and XS writers to understand this support and make sure that the code they write does not corrupt Unicode data. =head2 Unicodeっていったい何? In the olden, less enlightened times, we all used to use ASCII. Most of us did, anyway. The big problem with ASCII is that it's American. Well, no, that's not actually the problem; the problem is that it's not particularly useful for people who don't use the Roman alphabet. What used to happen was that particular languages would stick their own alphabet in the upper range of the sequence, between 128 and 255. Of course, we then ended up with plenty of variants that weren't quite ASCII, and the whole point of it being a standard was lost. Worse still, if you've got a language like Chinese or Japanese that has hundreds or thousands of characters, then you really can't fit them into a mere 256, so they had to forget about ASCII altogether, and build their own systems using pairs of numbers to refer to one character. To fix this, some people formed Unicode, Inc. and produced a new character set containing all the characters you can possibly think of and more. There are several ways of representing these characters, and the one Perl uses is called UTF-8. UTF-8 uses a variable number of bytes to represent a character, instead of just one. You can learn more about Unicode at http://www.unicode.org/ =head2 UTF-8 文字列をどう認識すればいいのか You can't. This is because UTF-8 data is stored in bytes just like non-UTF-8 data. The Unicode character 200, (C<0xC8> for you hex types) capital E with a grave accent, is represented by the two bytes C. Unfortunately, the non-Unicode string C has that byte sequence as well. So you can't tell just by looking - this is what makes Unicode input an interesting problem. The API function C can help; it'll tell you if a string contains only valid UTF-8 characters. However, it can't do the work for you. On a character-by-character basis, C will tell you whether the current character in a string is valid UTF-8. =head2 UTF-8 がどうやって Unicode 文字を表現しているのか As mentioned above, UTF-8 uses a variable number of bytes to store a character. Characters with values 1...128 are stored in one byte, just like good ol' ASCII. Character 129 is stored as C; this continues up to character 191, which is C. Now we've run out of bits (191 is binary C<10111111>) so we move on; 192 is C. And so it goes on, moving to three bytes at character 2048. Assuming you know you're dealing with a UTF-8 string, you can find out how long the first character in it is with the C macro: char *utf = "\305\233\340\240\201"; I32 len; len = UTF8SKIP(utf); /* len is 2 here */ utf += len; len = UTF8SKIP(utf); /* len is 3 here */ Another way to skip over characters in a UTF-8 string is to use C, which takes a string and a number of characters to skip over. You're on your own about bounds checking, though, so don't use it lightly. All bytes in a multi-byte UTF-8 character will have the high bit set, so you can test if you need to do something special with this character like this (the UTF8_IS_INVARIANT() is a macro that tests whether the byte can be encoded as a single byte even in UTF-8): U8 *utf; UV uv; /* Note: a UV, not a U8, not a char */ if (!UTF8_IS_INVARIANT(*utf)) /* Must treat this as UTF-8 */ uv = utf8_to_uv(utf); else /* OK to treat this character as a byte */ uv = *utf; You can also see in that example that we use C to get the value of the character; the inverse function C is available for putting a UV into UTF-8: if (!UTF8_IS_INVARIANT(uv)) /* Must treat this as UTF8 */ utf8 = uv_to_utf8(utf8, uv); else /* OK to treat this character as a byte */ *utf8++ = uv; You B convert characters to UVs using the above functions if you're ever in a situation where you have to match UTF-8 and non-UTF-8 characters. You may not skip over UTF-8 characters in this case. If you do this, you'll lose the ability to match hi-bit non-UTF-8 characters; for instance, if your UTF-8 string contains C, and you skip that character, you can never match a C in a non-UTF-8 string. So don't do that! =head2 Perl はどのように UTF-8 文字列を格納しているのか Currently, Perl deals with Unicode strings and non-Unicode strings slightly differently. If a string has been identified as being UTF-8 encoded, Perl will set a flag in the SV, C. You can check and manipulate this flag with the following macros: SvUTF8(sv) SvUTF8_on(sv) SvUTF8_off(sv) This flag has an important effect on Perl's treatment of the string: if Unicode data is not properly distinguished, regular expressions, C, C and other string handling operations will have undesirable results. The problem comes when you have, for instance, a string that isn't flagged is UTF-8, and contains a byte sequence that could be UTF-8 - especially when combining non-UTF-8 and UTF-8 strings. Never forget that the C flag is separate to the PV value; you need be sure you don't accidentally knock it off while you're manipulating SVs. More specifically, you cannot expect to do this: SV *sv; SV *nsv; STRLEN len; char *p; p = SvPV(sv, len); frobnicate(p); nsv = newSVpvn(p, len); The C string does not tell you the whole story, and you can't copy or reconstruct an SV just by copying the string value. Check if the old SV has the UTF-8 flag set, and act accordingly: p = SvPV(sv, len); frobnicate(p); nsv = newSVpvn(p, len); if (SvUTF8(sv)) SvUTF8_on(nsv); In fact, your C function should be made aware of whether or not it's dealing with UTF-8 data, so that it can handle the string appropriately. Since just passing an SV to an XS function and copying the data of the SV is not enough to copy the UTF-8 flags, even less right is just passing a C to an XS function. =head2 文字列から UTF-8 への変換 If you're mixing UTF-8 and non-UTF-8 strings, you might find it necessary to upgrade one of the strings to UTF-8. If you've got an SV, the easiest way to do this is: sv_utf8_upgrade(sv); However, you must not do this, for example: if (!SvUTF8(left)) sv_utf8_upgrade(left); If you do this in a binary operator, you will actually change one of the strings that came into the operator, and, while it shouldn't be noticeable by the end user, it can cause problems. Instead, C will give you a UTF-8-encoded B of its string argument. This is useful for having the data available for comparisons and so on, without harming the original SV. There's also C to go the other way, but naturally, this will fail if the string contains any characters above 255 that can't be represented in a single byte. =head2 他に知っておくべきこと Not really. Just remember these things: =over 3 =item * There's no way to tell if a string is UTF-8 or not. You can tell if an SV is UTF-8 by looking at is C flag. Don't forget to set the flag if something should be UTF-8. Treat the flag as part of the PV, even though it's not - if you pass on the PV to somewhere, pass on the flag too. =item * If a string is UTF-8, B use C to get at the value, unless C in which case you can use C<*s>. =item * When writing a character C to a UTF-8 string, B use C, unless C in which case you can use C<*s = uv>. =item * Mixing UTF-8 and non-UTF-8 strings is tricky. Use C to get a new string which is UTF-8 encoded. There are tricks you can use to delay deciding whether you need to use a UTF-8 string until you get to a high character - C is one of those. =back =head1 カスタムオペレータ Custom operator support is a new experimental feature that allows you to define your own ops. This is primarily to allow the building of interpreters for other languages in the Perl core, but it also allows optimizations through the creation of "macro-ops" (ops which perform the functions of multiple ops which are usually executed together, such as C.) This feature is implemented as a new op type, C. The Perl core does not "know" anything special about this op type, and so it will not be involved in any optimizations. This also means that you can define your custom ops to be any op structure - unary, binary, list and so on - you like. It's important to know what custom operators won't do for you. They won't let you add new syntax to Perl, directly. They won't even let you add new keywords, directly. In fact, they won't change the way Perl compiles a program at all. You have to do those changes yourself, after Perl has compiled the program. You do this either by manipulating the op tree using a C block and the C module, or by adding a custom peephole optimizer with the C module. When you do this, you replace ordinary Perl ops with custom ops by creating ops with the type C and the C of your own PP function. This should be defined in XS code, and should look like the PP ops in C. You are responsible for ensuring that your op takes the appropriate number of values from the stack, and you are responsible for adding stack marks if necessary. You should also "register" your op with the Perl interpreter so that it can produce sensible error and warning messages. Since it is possible to have multiple custom ops within the one "logical" op type C, Perl uses the value of C<< o->op_ppaddr >> as a key into the C and C hashes. This means you need to enter a name and description for your op at the appropriate place in the C and C hashes. Forthcoming versions of C (version 1.0 and above) should directly support the creation of custom ops by name. =head1 著者 Until May 1997, this document was maintained by Jeff Okamoto Eokamoto@corp.hp.comE. It is now maintained as part of Perl itself by the Perl 5 Porters Eperl5-porters@perl.orgE. With lots of help and suggestions from Dean Roehrich, Malcolm Beattie, Andreas Koenig, Paul Hudson, Ilya Zakharevich, Paul Marquess, Neil Bowers, Matthew Green, Tim Bunce, Spider Boardman, Ulrich Pfeifer, Stephen McCamant, and Gurusamy Sarathy. =head1 関連項目 perlapi(1), perlintern(1), perlxs(1), perlembed(1)