Regular Expression 正则表达式-3 (C++)

最后用C++实现了一把，因为STL中尚未包含Regular Expression，因此我使用了Boost中的Regex++。不过因为不是很熟悉，所以代码很蹩脚，将就看了。呵呵。

#include <string>
#include <boost/regex.hpp>
#include <iostream>
#include <fstream>

using namespace std;

void readFile( const char* filename, string& str );
void writeFile( const char* filename, const string str );
void filter( const string input, string& output );

int main(int argc, const char* argv[])
{
    if( argc < 3 )
    {
        cout<< "Please enter 2 filenames(e.g. In.txt Out.txt)" << endl;
        return 1;
    }
    string strIn, strOut;

    readFile( argv[1], strIn );
    filter( strIn, strOut );
    writeFile( argv[2], strOut );
}

void readFile( const char* filename, string& str )
{
    ifstream in( filename );
    str.erase();
    str.reserve( in.rdbuf()->in_avail() );
    string strTemp;
    while( !in.eof() )
    {
        in >> strTemp;
        str.append(strTemp);
    }
    in.close();
}

void writeFile( const char* filename, const string str )
{
    ofstream out( filename );
    out.write( str.c_str(), (streamsize)str.length() );
    out.flush();
    out.close();
}
void filter( const string input, string& output )
{
    output.erase();
    output.reserve( input.length() );

    boost::regex expression("\"(\\w+):(\\w+)%(\\w+)\"");
    boost::smatch group;
    boost::regex_constants::match_flag_type flags = boost::regex_constants::match_default;

    string::const_iterator start, end;
    start = input.begin();
    end = input.end();

    while( boost::regex_search( start, end, group, expression, flags ))
    {
        output.append( group[1] );
        output.append( ":" );
        output.append( group[2] );
        output.append( "*" );
        output.append( group[3] );
        output.append( "," );
        output.append( "\n" );
        // update
        start = group[0].second;
        flags |= boost::regex_constants::match_prev_avail;
        flags |= boost::regex_constants::match_not_bob;
    }
    return;
}