c++中string与int之间相互转换

std::string char2str( int in_ch=-1)
    {        
        char ch_buff[4];
        memset(ch_buff,0,4);    
        sprintf(ch_buff,"%d",in_ch);
        //itoa( in_ch,ch_buff,4);

        std::string str(ch_buff);        
        return str;
    }

    char str2char(std::string str)
    {
        char ret=0;
        if( !str.empty() )
        {
            ret= atoi( str.c_str() );
            return ret;
        }
        return -1;
    }