C语言实验，编写一字符串移动函数

编写一字符串移动函数 char*shift ( char*pstr , int n , char* mode ),该函数的功能是:(1)当 mode = R 时,将字符串 pstr 循环右移n位:(2)当 mode=L 时,将字符串 pstr 循环左移n位返回值为移位后的字符串的首地址。例如:字符串“12345678”,循环右移3位将得到“67812345”循环左移3位将得到“45678123”

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

char *shift(char *pstr, int n, char *mode)
{
    int len = strlen(pstr);
    char *tmp = (char *)calloc(n, sizeof(char));
    char *strs = (char *)calloc(len, sizeof(char));

    int sublen = len - n;

    if (*mode == 'L')
    {
        memcpy(tmp, pstr, n);
        memcpy(strs, pstr + n, sublen);
        memcpy(strs + sublen, tmp, n);
    }
    else
    {
        memcpy(tmp, pstr + sublen, n);
        memcpy(strs, tmp, n);
        memcpy(strs + n, pstr, sublen);
    }

    free(tmp);

    return strs;
}

int main()
{
    char *p, *str = "12345678";

    p = shift(str, 3, "L");
    printf("%s\n", p);
    free(p);

    p = shift(str, 3, "R");
    printf("%s\n", p);
    free(p);

    return 0;
}