int code_convert(const char *from_charset,const char *to_charset,const char *inbuf,size_t inlen,char *outbuf,size_t outlen)
{
    iconv_t cd;
    const char *temp = inbuf;
    const char **pin = &temp;
    char **pout = &outbuf;
    memset(outbuf,outlen);
    
    cd = iconv_open(to_charset,from_charset);
    if (cd == 0) return -1;
    if (iconv(cd,(char **)pin,&inlen,pout,&outlen) == -1) return -1;
    iconv_close(cd);
    return 0;
}

GBK 转 UTF-8

std::string a2u(const char *inbuf)
{
    size_t inlen = strlen(inbuf);
    char * outbuf = new char[inlen * 2 + 2];
    std::string strRet;
    if (code_convert("GBK","UTF-8",inbuf,inlen,outbuf,inlen * 2 + 2) == 0)
    {
        strRet = outbuf;
    }
    delete[] outbuf;
    return strRet;
}

std::string u2a(const char *inbuf)
{
    size_t inlen = strlen(inbuf);
    char * outbuf = new char[inlen * 2 + 2];
    std::string strRet;
    if (code_convert("UTF-8","GBK",inlen * 2 + 2) == 0)
    {
        strRet = outbuf;
    }
    delete[] outbuf;
    return strRet;
}