字符串反转

int revstr(char *str)
{
    char ch;
    char *start = str;
    char *end = str;
    if(str == NULL)
        return -1;
    while(*end)
        end++;
    end -= 1;
    while(start < end)
    {
        ch = *start;
        *start++ = *end;
        *end-- = ch;
    }
    return 0;
}