字符串反转

定义首尾两个指针，交换指针指向的值

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;
}
}
return str;
}