Open System Services Library Calls Reference Manual (G06.29+, H06.08+, J06.03+)

opendir(3) OSS Library Calls Reference Manual
NAME
opendir - Opens a directory and creates a directory stream
LIBRARY
G-series native OSS processes: /G/system/sysnn/zossfsrl
32-bit H-series and J-series OSS processes: /G/system/zdllnnn/zossfdll |
64-bit H-series and J-series OSS processes: /G/system/zdllnnn/yossfdll |
SYNOPSIS
#include <sys/types.h> /* optional except for POSIX.1 */
#include <dirent.h>
DIR *opendir(
const char *dir_name);
PARAMETERS
dir_name Names the directory. If the final component of dir_name names a symbolic link,
the link will be traversed and pathname resolution will continue.
DESCRIPTION
The opendir( ) function opens the directory designated by the dir_name parameter and associates
a directory stream with it. The directory stream is positioned at the first entry. The type DIR,
which is defined in the dirent.h header file, represents a directory stream, which is an ordered
sequence of all the directory entries in a particular directory. (Directory streams are not imple-
mented through file descriptors.)
The opendir( ) function returns a pointer to identify the directory stream in subsequent opera-
tions. The null pointer is returned when the directory named by the dir_name parameter cannot
be accessed or when not enough memory is available to hold the buffer stream.
The opendir( ) function does not update the st_atime field of the opened directory.
An open directory should always be closed with the closedir( ) function to ensure the freeing of
resources held by the stream.
When one of the set of exec, tdm_exec,ortdm_spawn functions is called, all open directory
streams are closed automatically. (For calls to tdm_spawn functions, only the directory streams
of the child process are closed.) The effect is the same as if the closedir( ) function had been
called for each open directory stream.
General Considerations for Directory Operations
Directory entries represent files. Files can be removed from a directory or added to a directory
asynchronously to the operation of the readdir( ) function.
If files are removed from a directory after the most recent call to the opendir( ) or rewinddir( )
function but prior to the first call to the readdir( ) function, the readdir() function does not
return entries for these files. If files are added to a directory after the most recent call to the
opendir( ) or rewinddir( ) function but prior to the first call to the readdir( ) function, the read-
dir( ) function returns entries for these files.
The readdir( ) function retrieves a block of directory entries with each actual read operation and
stores them in a system buffer. The readdir() function marks for update the st_atime field of the
directory each time the directory is actually read.
The first call to the readdir( ) function after a call to the opendir( ) or rewinddir( ) function
retrieves a block of directory entries. The first two entries of the block are for . (dot) and ..(dot-
dot). Therefore, the first entry returned is for . (dot). Each subsequent call to readdir( ) fetches
another entry from the buffer until the buffer is empty, at which time another block of entries is
automatically retrieved.
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