试了一把PCRE

虽然我在C++里用正则表达式已经有一些年头了，不过一直都是用的boost里那个库。坦白说，不是很好用。虽然我很早就知道PCRE，但一直都以为这是一个为PHP开发的库。实在是火星人啊。囧

前两天在推土上提起这事时，火炬向我推荐说PCRE比boost里那个正则库好用，于是试了一下，结果可耻滴发现BCB自带了PCRE，只不过没有在文档里提到罢了。

不 过PCRE是一个C语言的库，用起来不够方便。虽然也有PCRE++这种C++封装的版本，但是只提供了GNU编译配置，移植到BCB里估计比较麻烦，因 为我用到的功能也不多，就自己做了个简单的封装，用了一些VCL的AnsiString/StringList之类。用起来方便不少。

#include <pcre.h>

class TPCRE
{
private:
    AnsiString FPattern;
    pcre * FRE;
    TStrings * FMatches;

public:
  __fastcall TPCRE(AnsiString aPattern="");
  __fastcall ~TPCRE();

  void __fastcall compile(AnsiString aPattern="");
  int  __fastcall exec(AnsiString aStr);  //  return matched count
  AnsiString __fastcall repeat_replace(AnsiString aStr, AnsiString aRepStr="");

  __property TStrings * Matches = { read = FMatches };
};

__fastcall TPCRE::TPCRE(AnsiString aPattern)
    : FRE(NULL), FMatches(new TStringList())
{
    FPattern = aPattern;
    if ( FPattern != "" )
        compile();
}

__fastcall TPCRE::~TPCRE()
{
    if (FRE)
        free(FRE);
    delete FMatches;
}

void __fastcall TPCRE::compile(AnsiString aPattern)
{
    if ( aPattern != "" )
        FPattern = aPattern;
    const char * error;
    int erroffset;
    if (FRE)
        free(FRE);
    FRE = pcre_compile(FPattern.c_str(), 0, &error, &erroffset, NULL);
    // if ( FRE == NULL )
    // PCRE compilation failed at offset %d: %s, erroffset, error
}

int __fastcall TPCRE::exec(AnsiString aStr)
{
    if (!FRE)
        throw Exception("No pattern or have not be compiled!");
    const int OVECCOUNT = 30;
    int ovector[OVECCOUNT];
    int rc = pcre_exec(FRE, NULL, aStr.c_str(), aStr.Length(), 0, ovector, OVECCOUNT);
    if (rc < 0) {
        if (rc == PCRE_ERROR_NOMATCH)
            throw Exception("Sorry, no match ...");
        else
            throw Exception(AnsiString("Matching error ") + IntToStr(rc));
    }
    // OK, has matched ...
    FMatches->Clear();
    for (int i = 0; i < rc; i++)
        FMatches->Add(aStr.SubString(
            ovector[2*i]+1, ovector[2*i+1]-ovector[2*i]));
    return rc;
}

AnsiString __fastcall TPCRE::repeat_replace(AnsiString aStr, AnsiString aRepStr)
{
    if (!FRE)
        throw Exception("No pattern or have not be compiled!");
    const int OVECCOUNT = 30;
    int ovector[OVECCOUNT];
    int rc=1;
    char *p = aStr.c_str();
    int n = 1;
    int len = aStr.Length();
    AnsiString s="";
    while (rc>0) {
        rc = pcre_exec(FRE, NULL, p, len, 0, ovector, OVECCOUNT);
        if (rc < 0) {
            if (rc == PCRE_ERROR_NOMATCH) {
                if (s=="")
                    s = aStr;
                else
                    s += aStr.SubString(n,aStr.Length()-n+1);
                break;
            }
            else
                throw Exception(AnsiString("Matching error ") + IntToStr(rc));
        }
        // OK, has matched ...
        s += aStr.SubString(n,ovector[0])+aRepStr;
        n += ovector[1];
        p = aStr.c_str()+n-1;
        len = aStr.Length()-n+1;
    }
    return s;
}

用法很简单，这是一段示例代码，可以把HTML转换成TXT：

// 输入：const char *s
// 输出：AnsiString sResult
    std::auto_ptr<TPCRE> re(new TPCRE("(?ims)<title>([^<]*)"));
    AnsiString sResult;
    if (re->exec(s)>1)
        sResult = re->Matches->Strings[1].Trim();
    re->compile("(?ims)<body[^>]*>(.*)");
    if (re->exec(s)>1) {
        AnsiString str = re->Matches->Strings[1].Trim();
        str = StringReplace(str,"\r","",TReplaceFlags()<<rfReplaceAll);
        str = StringReplace(str,"\n","",TReplaceFlags()<<rfReplaceAll);
        str = StringReplace(str,"&nbsp;"," ",TReplaceFlags()<<rfReplaceAll);
        //  replace <br /> to \r\n
        re->compile("(?i)<br\s*/?>");
        str = re->repeat_replace(str,"\r\n");
        //  remove <script...>...</script>
        re->compile("(?ims)<script[^>]*>.*</script>");
        str = re->repeat_replace(str);
        //  remove <!-- ... -->
        re->compile("(?ims)<!--.*-->");
        str = re->repeat_replace(str);
        //  remove <...>
        re->compile("(?ims)<[^>]*>");
        str = re->repeat_replace(str);
        sResult += str;
    }

主要就是取出title部分和body部分，然后将body部分的回车全部去掉， 替换成空格，br换成回车，脚本和注释去掉，最后去掉所有HTML的标记。