Orders c++生成全排列

/*将源字符串的顺序改变为升序，课生成字典序上升的全排列。*/#include<stdio.h>#include<string.h>#include <algorithm>using namespace std;int cmp(const void *a,const void *b){    return *(char *)a-*(char *)b;}int main(){    int i;    char a[300];    while(scanf("%s",a)==1)    {        int len=strlen(a);        qsort(a,len,sizeof(a[0]),cmp);        do        {            for(i=0; i<len; i++) printf("%c",a[i]);            printf("\n");        }        while (next_permutation(a,a+len));    }    return 0;}