Source Insight完美转换UTF-8 到 GB2312

/*! detect if the fiel is UTF-8 code
\param LPCTSTR filename
\return true/false
*/
bool detect_utf8file(LPCTSTR filename)
{
    const unsigned char BOM[3] = {0xEF,0xBB,0xBF};
    int count_good_utf = 0;
    int count_bad_utf = 0;
    int begin = 0;
    char buf[3]={0,};
    CStdioFile file_r ;
    if(!file_r.Open((char*)(LPCTSTR)filename, CStdioFile::modeReadWrite))
        return false;

    file_r.Read(buf,3);
    if(!strncmp(buf,(char *)BOM,3)) {
        std::cout<<"this is utf(BOM). "<<endl;
        file_r.Close();
        return true;
    }
    else { // detect the whole file 
    //    UTF-8 text encoding auto-detection
    //    count the following pairs of consecutive bytes as shown in the table:
    //    11..    10..    good
    //    00..    10..    bad
    //    10..    10..    don‘t care
    //    11..    00..    bad
    //    11..    11..    bad
    //    00..    00..    don‘t care
    //    10..    00..    don‘t care
    //    00..    11..    don‘t care
    //    10..    11..    don‘t care
        char current_byte,previous_byte;
        file_r.SeekToBegin();
        file_r.Read(&current_byte,1);
        previous_byte = current_byte;
        while(file_r.Read(&current_byte,1)) {
            if ((current_byte & 0xC0) == 0x80) {
                if ((previous_byte & 0xC0) == 0xC0) {
                    count_good_utf ++;
                } else if ((previous_byte & 0x80) == 0x00) {
                    count_bad_utf ++;
                }
            } else if ((previous_byte & 0xC0) == 0xC0 ){
                count_bad_utf ++;
            }
            previous_byte = current_byte;
        }
        //    the comparison ">=" handles pure ASCII files as UTF-8,
        //    replace it with ">" to change that

        if(count_good_utf > count_bad_utf) {
            file_r.Close();
            std::cout<<"the code of this file is utf(no BOM). "<<endl;
            return true;
        } else if(count_good_utf == count_bad_utf) {
            file_r.Close();
            std::cout<<"the code of this file is pure ASCII file as UTF-8. "<<endl;    
            return true;
        }
        else {
            file_r.Close();
            std::cout<<"the code of this file is not utf. "<<endl;
            return false;    
        }
    }
}