用4种不同的方法反转字符串

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
void strrev_v1(char* src) {
assert(src != NULL);
if (strlen(src) == 1)
return;
char *head = src;
char *tail = src + strlen(src) - 1;
char temp = ' ';
while(head < tail) {
temp = head[0];
head[0] = tail[0];
tail[0] = temp;
head++;
tail--;
}
}

void strrev_v2(char* src) {
assert(src != NULL);
if (strlen(src) == 1)
return;
char *head = src;
char *tail = src + strlen(src) - 1;
while(head < tail) {
head[0] ^= tail[0];
tail[0] ^= head[0];
head[0] ^= tail[0];
head++;
tail--;
}
}

void strrev_v3(char* src) {
assert(src != NULL);
if (strlen(src) == 1)
return;
char *head = src;
char *tail = src + strlen(src) - 1;
while(head < tail) {
head[0] = head[0] + tail[0];
tail[0] = head[0] - tail[0];
head[0] = head[0] - tail[0];
head++;
tail--;
}
}

void strrev_v4(char* src, int len) {     //采用的是递归的思路
assert(src != NULL);
if (len < 2)
return;
char *head = src;
char *tail = src + len - 1;
head[0] = head[0] + tail[0];
tail[0] = head[0] - tail[0];
head[0] = head[0] - tail[0];
strrev_v4(head+1, len-2);
}

int main() {
char *a = (char*)malloc(5*sizeof(char));    //本来这里采用的是char *a = "12345"的写法，后来发现"12345"是常量字符串，不能被修改，当然就不能被交换了。
strcpy(a, "12345");
strrev_v4(a, strlen(a));
printf("%s/n", a);
return 0;
}