ゆとりーなの日記

日記的な事を書いて行くと思はれる

なにかまちがえた?

win32APIにはOutputDebugStringという名の関数が用意されています。この子はデバッガのストリームに出力してくれる関数です。

#include <windows.h>

int main() {
    const char * const str("Hello World!\n");
    OutputDebugString(str);
    return 0;
}

これでデバッガ出力には、

// 色々それっぽいメッセージが出てくる
Hello World!
// 色々それっぽいメッセージが出てくる

と出てくれます。色々それっぽいメッセージっていうのは、所謂シンボルが読み込まれましたとか、終了しましたとかのあれです。
で、Boost.iostreamを使ってOutputDebugStringする自作ストリームを作ってみようと思い立ったのでやってみました。

#include <boost/iostreams/stream.hpp>
#include <windows.h>

class odstream : public boost::iostreams::sink {
 public:
     std::streamsize write(const char * const s, const std::streamsize n) {
         OutputDebugString(s);
         return n;
     }
};

int main() {
    odstream od;
    boost::iostreams::stream<odstream> s(od);
    s << "Hello World!" << std::endl;
    return 0;
}

デバッガ出力には、

// 色々それっぽいメッセージが出てくる
Hello World!
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何かがおかしいです。
一応VC++2010側がこんな警告を出してくるのでひょっとしてこれが影響してるのかもしれませんが・・・。

d:\boost\boost\iostreams\detail\buffer.hpp(151): warning C4244: '引数' : 'std::streamsize' から 'std::allocator<_Ty>::size_type' への変換です。データが失われる可能性があります。

さてさてどうしたものか。
あとこれboost.1.4.2なんですけど、最近出たboost.1.4.3にしたら直ったりするんですかね。
追記:
egtra氏の指摘を受け、以下の様にコードを修正したところ怪しい文字列が出てくることはなくなりました。

#include <vector>
#include <boost/iostreams/stream.hpp>
#include <windows.h>

class odstream : public boost::iostreams::sink {
 public:
     std::streamsize write(const char * const s, const std::streamsize n) {
        std::vector<char> temp(n + 1);
        lstrcpyn(&temp.front(), s, n);
        lstrcat(&temp.front(), "\0");
        OutputDebugString(&temp.front());
        return n;
     }
};

int main() {
    odstream od;
    boost::iostreams::stream<odstream> s(od);
    s << "Hello World!\n" << std::endl;
    return 0;
}

'\0'付ける部分とかは結構適当に書いたのでそこら辺はスルーしてください。で、デバッグ出力の方は、

// 色々それっぽいメッセージが出てくる
Hello World!
// 色々それっぽいメッセージが出てくる

となり無事解決です。といいたいところなのですが、"Hello World!"の最後に"\n"を入れないとどうやら改行してくれないみたいです。std::endlだけで改行させるにはどうしたらいいのかがまだ謎として残っています。