（被考了一题遍历目录，连需要的系统库函数我都不知道...打击中...）
小羽给了一个答案：
#include<stdio.h>
#include<dirent.h>
int main(int argc,char **argv)
{
  DIR  *p;
  struct dirent *dirp;
  if (argc != 2)
   {
     printf("the director name  is requried");
     exit(0);
    }
  if ((p = opendir(argv[1])) == NULL)
  {
   printf("not open %s",argv[1]);
   exit(0);
  }
  while( (dirp = readdir(p)) != NULL)
   printf("%s\n",dirp -> d_name);
  closedir(p);
 exit(0);
}
知道需要dirent.h这个头文件，里面有几个函数还有dir目录结构体的定义。
在网上找了篇写的还蛮详细的，特此转载~~
LINUX下历遍目录的方法一般是这样的
打开目录-》读取-》关闭目录
相关函数是
opendir -> readdir -> closedir

#include <dirent.h>
DIR *opendir(const char *dirname);


#include <dirent.h>
struct dirent *readdir(DIR *dirp);


#include <dirent.h>
int closedir(DIR *dirp);

好了，三个函数都出来了呵呵，原型就是上面，给自己解释一下免得以后我自己忘了呵呵！我以经忘过好几回了，所以这次放上博客来
opendir用于打开目录，是类似于流的那种方式，返回一个指向DIR结构体的指针他的参数*dirname是一个字符数组或者字符串常量,
readdir函数用于读取目录，他只有一个参数，这个参数主opendir返回的结构体指针，或者叫句柄更容易理解些吧。这个函数也返回一个结构体指针 dirent *
dirent的结构如下定义
                   struct dirent
                   {
                       long d_ino;                      /* inode number */
                       off_t d_off;                     /* offset to this dirent */
                       unsigned short d_reclen;         /* length of this d_name */
                       char d_name [NAME_MAX+1];        /* file name (null-terminated) */
                   }
结构体中d_ino存放的是该文件的结点数目，什么是结点数目呢我也说不清楚了呵呵，查一下其它资料了(这里应该不是节点数目，而是其下文件的索引节点号inode)
d_off 是文件在目录中的编移，具体是什么意思我也不是很明白，我很少用到它，其本上就是用到d_name ，short d_reclen是这个文件的长度，需要注意的是这里的长度并不是指文件大小，因为大小和长度是2回事了，你可以用lseek将文件长度移得很长，但大小其实还是那么大.最后一个元素就是我们要的了，文件名称！
写了一个实例:

/**
* 功能：       Linux下C语言目录历遍 (读取目录)
* 作者：       小徐
* 邮箱：      xjtdy888@163.com
* QQ:          339534039
* 转载请注明出处
*/
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
#include <dirent.h>

void print_usage(void);

void print_usage(void)
{
printf("Usage: test dirname\n");
}

int main(int argc,char *argv[])
{
DIR * dp;
struct dirent *filename;

if (argc < 2)
{
       print_usage();
       exit(1);
}

dp = opendir(argv[1]);
if (!dp)
{
       fprintf(stderr,"open directory error\n");
       return 0;
}
while (filename=readdir(dp))
{
       printf("filename:%-10s\td_info:%ld\t d_reclen:%us\n",
         filename->d_name,filename->d_ino,filename->d_reclen);
}
closedir(dp);
return 0;
}

将上面代码保存为readdir.c执行下面的命令进行编译测试
[root@phpos ~]# gcc readdir.c
[root@phpos ~]# ./a.out
Usage: test dirname
[root@phpos ~]# ./a.out /etc/samba/
filename:lmhosts             d_info:49296          d_reclen:24s
filename:smb.conf            d_info:49825          d_reclen:24s
filename:smbpasswd           d_info:49402          d_reclen:24s
filename:..                  d_info:47906          d_reclen:16s
filename:secrets.tdb         d_info:49812          d_reclen:24s
filename:.                   d_info:49295          d_reclen:16s
filename:smbusers            d_info:49377          d_reclen:24s
[root@phpos ~]# ./a.out /var/
filename:preserve            d_info:31971          d_reclen:24s
filename:lock                d_info:31966          d_reclen:16s
filename:yp                  d_info:31976          d_reclen:16s
filename:empty               d_info:31962          d_reclen:24s
filename:run                 d_info:31972          d_reclen:16s
filename:lib                 d_info:31939          d_reclen:16s
filename:nis                 d_info:31969          d_reclen:16s
filename:local               d_info:31965          d_reclen:24s
filename:spool               d_info:31973          d_reclen:24s
filename:tmp                 d_info:31941          d_reclen:16s
filename:opt                 d_info:31970          d_reclen:16s
filename:log                 d_info:31959          d_reclen:16s
filename:crash               d_info:31997          d_reclen:24s
filename:..                  d_info:2              d_reclen:16s
filename:account             d_info:32037          d_reclen:24s
filename:mail                d_info:31968          d_reclen:16s
filename:cache               d_info:31960          d_reclen:24s
filename:db                  d_info:31961          d_reclen:16s
filename:.                   d_info:31938          d_reclen:16s
[root@phpos ~]#
程序正常执行!到此完了呵呵!！