给出一个函数来输出一个字符串的所有排列

#include <stdio.h>

void permutation(char * p_str, char * p_begin)
{
    if(!p_str || !p_begin)
    {
        return;
    }
 
    /*
 * If p_begin points to the end of string,
 * this round of permutation is finished,
 * print the permuted string.
 */
    if('\0' == *p_begin)
    {
        printf("%s\n", p_str);
    }
    /* Otherwise, permute string. */
    else
    {
        char * p_ch;
  
        for(p_ch = p_begin; *p_ch != '\0'; ++p_ch)
        {
            char temp;
   
            /* Swap p_ch and p_begin. */
            temp = *p_ch;
            *p_ch = *p_begin;
            *p_begin = temp;
   
            permutation(p_str, p_begin + 1);
   
            /* Restore p_ch and p_begin. */
            temp = *p_ch;
            *p_ch = *p_begin;
            *p_begin = temp;
        }
    }
}

int main(int argc, char * argv[])
{
    
    
    char strr[4]="123";
    char strd[4];
 permutation(strr, strr);
    return 0;
}