字符串翻转函数

#include <string.h>
#include <stdio.h>
#include <stdlib.h>

/*功能：递归实现字符串的反转*/

char * reverse3(char * str)
{
    if(str == NULL)
        return NULL;
    int len=strlen(str);
    if(len > 1)
    {
        char ctemp=str[0];
        str[0]=str[len-1];
        str[len-1]='\0';

        reverse3(str+1);
        str[len-1]=ctemp;
    }
    return str;
}

char * reverse2(char * str)
{
    if(str == NULL)
        return NULL;
    int len = strlen(str);
    if(len > 1)
    {
        char temp = str[0];
        str[0] = str[len-1];
        str[len-1] = temp;

        char newstr[len+1];
        memset(newstr, 0, sizeof(newstr));
        int newlen = strlen(str) - sizeof(char)*2;
        if(newlen > 1)
        {
            memcpy(newstr, str+sizeof(char)*1, sizeof(char)*newlen);
            reverse2(newstr);
            memcpy(str+sizeof(char)*1, newstr, sizeof(char)*newlen);
        }
    }
    return str;
}

/*功能：非递归实现字符串的反转*/
char * reverse1(char * str)
{
    if(str == NULL)
        return NULL;
    char * head = str;
    char * tail = str + strlen(str) -1;
    char temp;
    while(head < str + strlen(str)/2)
    {
        temp = *head;
        *head++ = *tail;
        *tail-- = temp;
    }
    return str;
}

int main(int argc, char * * argv)
{
    printf("***********************************\n");
    char str1[1024];
    memset(str1, 0, sizeof(str1));
    strcpy(str1, "wangxiancai!");
    printf("str1 = [%s]\n", str1);
    reverse1(str1);
    printf("str1 = [%s]\n", str1);

    printf("***********************************\n");
    char str2[1024];
    memset(str2, 0, sizeof(str2));
    strcpy(str2, "123");
    printf("str2 = [%s]\n", str2);
    reverse2(str2);
    printf("str2 = [%s]\n", str2);
    printf("***********************************\n");

    char str3[1024];
    memset(str3, 0, sizeof(str3));
    strcpy(str3, "12345678");
    printf("str3 = [%s]\n", str3);
    reverse3(str3);
    printf("str3 = [%s]\n", str3);
    printf("***********************************\n");

    return 0;
}