删除字符串的前后小于等于空格的ascii

char *trim_befor_after20 (char *str)
{
    char    *tmp;
    char    *tmp1;

    tmp=str;
    tmp1=str;

    if(*str==0x00)
        return(tmp1);

    while ((unsigned char)*str>0x00 && (unsigned char)*str<=0x20) { str++; }

    while ((unsigned char)*str!='\0')
    {
        if((unsigned char)*str>0x00 && (unsigned char)*str<0x20)
        {
            str++;
        }
        else
        {
            *tmp=*str; str++; tmp++;
        }
    }

    str=tmp;

    str--;
    while ((unsigned char)*str>0x00 && (unsigned char)*str<=0x20) { str--; }

    str++;
    *str='\0';
    return tmp1;
}