1.首先要打开目录文件
DIR *opendir( const char *name);
DIR *fdopendir( int fd);
2.读取目录文件信息的函数
注意：这是个库函数
struct dirent *readdir( DIR *dirp);
int readdir_r( DIR *dirp, struct dirent *entry, struct dirent **result);
文件目录结构体：
struct dirent {ino_t d_ino; /* inode number 索引节点号*/off_t d_off; /* not an offset; see NOTES 在目录文件中的偏移*/unsigned short d_reclen; /* length of this record 文件名长*/unsigned char d_type; /*type of file; not supported by all filesystem types 文件类型*/ char d_name[256]; /* filename 文件名，最长255字符*/};
d_type的值为：
DT_BLK This is a block device.
DT_CHR This is a character device.
DT_DIR This is a directory.
DT_FIFO This is a named pipe (FIFO).
DT_LNK This is a symbolic link.
DT_REG This is a regular file.
DT_SOCK This is a UNIX domain socket.
DT_UNKNOWN The file type is unknown.
readdir（）函数实例：
注意：
每次使用readdir后，readdir会读到下一个文件，readdir是依次读出目录中的所有文件，每次只能读一个
这个特性和readdir_r()一样
#include <stdio.h>
#include <sys/types.h>
#include <dirent.h>
int main(int argc, char **argv){DIR *pDir = NULL;struct dirent * pEnt = NULL;unsigned int cnt = 0; if (argc != 2){printf("usage: %s dirname\n", argv[0]);return -1;}pDir = opendir(argv[1]);if (NULL == pDir){perror("opendir");return -1;} while (1){pEnt = readdir(pDir);if(pEnt != NULL){if (pEnt->d_type == DT_REG){printf("是普通文件:");}else{printf("不是普通文件:");}printf("name：[%s] \n", pEnt->d_name);cnt++;}else{break;}};printf("总文件数为：%d\n", cnt);return 0;
}结果：
$ ./a.out .
是普通文件:name：[a.c]
不是普通文件:name：[.]
不是普通文件:name：[..]
是普通文件:name：[a.out]
不是普通文件:name：[12_sr]
不是普通文件:name：[10_sr]
不是普通文件:name：[17_sr]
不是普通文件:name：[15_sr]
不是普通文件:name：[14.sr]
不是普通文件:name：[18_sr]
不是普通文件:name：[udp]
不是普通文件:name：[16_sr]
不是普通文件:name：[tcp]
总文件数为：13readdir_r():
注意：
这三个参数
#include <stdio.h>
#include <sys/types.h>
#include <dirent.h>
#include <stdlib.h>
int main(int argc, char **argv)
{DIR *pDir = NULL;struct dirent * pEnt = NULL;struct dirent *entry = (struct dirent *)malloc(sizeof(struct dirent));struct dirent **result = (struct dirent **)malloc(sizeof(struct dirent));unsigned int cnt = 0;unsigned int ret = 0; if (argc != 2){printf("usage: %s dirname\n", argv[0]);return -1;}pDir = opendir(argv[1]);if (NULL == pDir){perror("opendir");return -1;}ret = readdir_r(pDir , entry , result);printf("return :%d \n", ret);printf("name :[%s] \n", entry->d_name);printf("name :[%s] \n", result[0]->d_name);ret = readdir_r(pDir , entry , result);printf("return :%d \n", ret);printf("name :[%s] \n", entry->d_name);printf("name :[%s] \n", result[0]->d_name);return 0;}结果：
