linux readdir

#include
#include
#include
#include
#include
#include

/*
 * readdir()函数返回一个指向目录结构的指针，该结构表示目录流中由p_dir指向的下一个目录条目。
 * 当到达目录流的末尾或发生错误时，它将返回NULL。
 */

#if 0 

struct dirent *readdir(DIR * p_dir);

struct dirent {
      ino_t      d_ino;   // 文件的inode
      off_t      d_off;   //  该文件相对于文件夹的偏移量
      unsigned short d_reclen;    // d_name的长度
      unsigned char  d_type;   //  文件类型, 例如管道, Socket , Block等
      char      d_name[256]; // 文件名
  };

The only fields in the dirent structure that are mandated by
       POSIX.1 are d_name and d_ino.  The other fields are
       unstandardized, and not present on all systems; see NOTES below
       for some further details.

       The fields of the dirent structure are as follows:

       d_ino  This is the inode number of the file.

       d_off  The value returned in d_off is the same as would be
              returned by calling telldir(3) at the current position in
              the directory stream.  Be aware that despite its type and
              name, the d_off field is seldom any kind of directory
              offset on modern filesystems.  Applications should treat
              this field as an opaque value, making no assumptions about
              its contents; see also telldir(3).

       d_reclen
              This is the size (in bytes) of the returned record.  This
              may not match the size of the structure definition shown
              above; see NOTES.

       d_type This field contains a value indicating the file type,
              making it possible to avoid the expense of calling
              lstat(2) if further actions depend on the type of the
              file.

              When a suitable feature test macro is defined
              (_DEFAULT_SOURCE on glibc versions since 2.19, or
              _BSD_SOURCE on glibc versions 2.19 and earlier), glibc
              defines the following macro constants for the value
              returned in d_type:

              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 could not be determined.

              Currently, only some filesystems (among them: Btrfs, ext2,
              ext3, and ext4) have full support for returning the file
              type in d_type.  All applications must properly handle a
              return of DT_UNKNOWN.

       d_name This field contains the null terminated filename.  See
              NOTES.

       The data returned by readdir() may be overwritten by subsequent
       calls to readdir() for the same directory stream.
#endif

static int test() 
{
    DIR * p_dir = NULL;
    struct dirent * dp = NULL;
    int len = -1;
    char *name = "aaaaa";

    // 通过opendir打开目录
    p_dir = opendir("/proc");
    if (p_dir == NULL) {
       return (-1);
    }

    len = strlen(name);

    //  开始遍历p_dir文件夹
    while ((dp = readdir(p_dir)) != NULL) {       
       printf("name:%s:%d\n", dp->d_name, dp->d_type);

       //  比较dp->d_name与name的值, 如果匹配则返回
       if (dp->d_reclen == len && strcmp(dp->d_name, name) == 0) {
            (void)closedir(p_dir);
            return 0;
       }
    }

    //  关闭dir
    (void)closedir(p_dir);

    return 0;
}

int main()
{
    test();

    return 0;
}