readdir

Name

opendir, readdir, readdir_r, telldir, seekdir, rewinddir, closedir, dirfd
- directory operations

Library

libc.lib

Synopsis

#include <sys/types.h>

#include <dirent.h>

DIR * opendir (const char *filename);

struct dirent * readdir (DIR *dirp);

int readdir_r (DIR *dirp, struct dirent *entry, struct dirent **result);

long telldir (DIR *dirp);

void seekdir (DIR *dirp, long loc);

void rewinddir (DIR *dirp);

int closedir (DIR *dirp);

int dirfd (DIR *dirp);

Return values

readdir function returns a pointer to a dirent structure, or NULL if an error occurs or end-of-file is reached.

Detailed description

The opendir function opens the directory named by filename, associates a directory stream with it and returns a pointer to be used to identify the directory stream in subsequent operations. The pointer NULL is returned if filename cannot be accessed, or if it cannot malloc enough memory to hold the whole thing.

The readdir function returns a pointer to the next directory entry. It returns NULL upon reaching the end of the directory or detecting an invalid seekdir operation.

The readdir_r function provides the same functionality as readdir, but the caller must provide a directory entry buffer to store the results in. If the read succeeds, result is pointed at the entry; upon reaching the end of the directory result is set to NULL. The readdir_r function returns 0 on success or an error number to indicate failure.

The telldir function returns the current location associated with the named directory stream. Values returned by telldir are good only for the lifetime of the DIR pointer, dirp, from which they are derived. If the directory is closed and then reopened, prior values returned by telldir will no longer be valid.

The seekdir function sets the position of the next readdir operation on the directory stream. The new position reverts to the one associated with the directory stream when the telldir operation was performed.

The rewinddir function resets the position of the named directory stream to the beginning of the directory.

The closedir function closes the named directory stream and frees the structure associated with the dirp pointer, returning 0 on success. On failure, -1 is returned and the global variable errno is set to indicate the error.

The dirfd function returns the integer file descriptor associated with the named directory stream, see open

Sample code which searches a directory for entry ‘‘name’’ is:

len = strlen(name);
dirp = opendir(".");
while ((dp = readdir(dirp)) != NULL)
        if (dp->d_namlen == len && !strcmp(dp->d_name, name)) {
                (void)closedir(dirp);
                return FOUND;
        }
(void)closedir(dirp);
return NOT_FOUND;
Note:
 Any changes happening to Directory after opendir call, will not be reflected by subsiquent readdir calls.

Examples

 /**
  * Detailed description: Sample usage of readdir call
  * Preconditions:  Example Directory should be present in current working directory
**/
#include <dirent.h>
#include  <unistd.h>
#include <sys/types.h>
int main()
{
  DIR *dirName;
  struct dirent *Dir;
  dirName = opendir("Example");
  if(dirName == NULL )  {
     printf("Failed to open directory \n");
     return -1;
  }
  if(!(Dir = readdir(dirName))  )  {
    printf("Read dir failed  \n");
    return -1;
  }
 printf("Directory Example read \n");
 closedir(dirName);
 return 0;
}

Output

Directory Example read