#include "apue.h"#include <dirent.h>int main(int argc, char* argv[]){    DIR* dp;    struct dirent* dirp;    if (argc != 2)        err_quit("usage: ls directory_name");    if ((dp = opendir(argv[1])) == NULL)    {        err_sys("can‘t open %s", argv[1]);    }    while ((dirp = readdir(dp)) != NULL)    {        printf("%s\n", dirp->d_name);    }    closedir(dp);    exit(0);}