字符串反转

char *revstr(char *str, size_t len)
{
    char    *start = str;
    char    *end = str + len - 1;
    char    ch;

    if (str != NULL)
    {
        while (start < end)
        {
            ch = *start;
            *start = *end;
            *end = ch;
            start++;
            end--;
        }
    }
    return str;
}

 详情参考：http://www.cnblogs.com/pianoid/archive/2011/10/30/string_reverse_in_c_language.html