NAME

dirname - report the parent directory name of a file pathname

SYNOPSIS

[XSI] #include <libgen.h>

char *dirname(char *path);

DESCRIPTION

The dirname() function shall take a pointer to a character string that contains a pathname, and return a pointer to a string that is a pathname of the parent directory of that file. Trailing '/' characters in the path are not counted as part of the path.

If path does not contain a '/', then dirname() shall return a pointer to the string ".". If path is a null pointer or points to an empty string, dirname() shall return a pointer to the string "." .

The dirname() function need not be reentrant. A function that is not required to be reentrant is not required to be thread-safe.

RETURN VALUE

The dirname() function shall return a pointer to a string that is the parent directory of path. If path is a null pointer or points to an empty string, a pointer to a string "." is returned.

The dirname() function may modify the string pointed to by path, and may return a pointer to static storage that may then be overwritten by subsequent calls to dirname().

ERRORS

No errors are defined.

EXAMPLES

The following code fragment reads a pathname, changes the current working directory to the parent directory, and opens the file.

char path[PATH_MAX], *pathcopy;
int fd;
fgets(path, PATH_MAX, stdin);
pathcopy = strdup(path);
chdir(dirname(pathcopy));
fd = open(basename(path), O_RDONLY);

Sample Input and Output Strings for dirname()

In the following table, the input string is the value pointed to by path, and the output string is the return value of the dirname() function.

Input String	Output String
"/usr/lib"	"/usr"
"/usr/"	"/"
"usr"	"."
"/"	"/"
"."	"."
".."	"."

Changing the Current Directory to the Parent Directory

The following program fragment reads a pathname, changes the current working directory to the parent directory, and opens the file.

#include <unistd.h>
#include <limits.h>
#include <stdio.h>
#include <fcntl.h>
#include <string.h>
#include <libgen.h>
...
char path[PATH_MAX], *pathcopy;
int fd;
...
fgets(path, PATH_MAX, stdin);
pathcopy = strdup(path);
chdir(dirname(pathcopy));
fd = open(basename(path), O_RDONLY);

APPLICATION USAGE

The dirname() and basename() functions together yield a complete pathname. The expression dirname(path) obtains the pathname of the directory where basename(path) is found.

Since the meaning of the leading "//" is implementation-defined, dirname(" //foo) may return either "//" or '/' (but nothing else).

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

basename(), the Base Definitions volume of IEEE Std 1003.1-2001, <libgen.h>

CHANGE HISTORY

First released in Issue 4, Version 2.

Issue 5

Moved from X/OPEN UNIX extension to BASE.

Normative text previously in the APPLICATION USAGE section is moved to the DESCRIPTION.

A note indicating that this function need not be reentrant is added to the DESCRIPTION.