NAME

basename — return the last component of a pathname

SYNOPSIS

[XSI]
#include <libgen.h>

char *basename(char *path);

DESCRIPTION

The basename () function shall take the pathname pointed to by path and return a pointer to the final component of the pathname, deleting any trailing ‘/’ characters.

If the string pointed to by path consists entirely of the ‘/’ character, basename () shall return a pointer to the string "/", except that if the string pointed to by path is exactly "//", it is implementation-defined whether "/" or "//" is returned.

If path is a null pointer or points to an empty string, basename () shall return a pointer to the string ".".

The basename () function may modify the string pointed to by path, and may return a pointer into the input string. The returned pointer might be invalidated if the input string is subsequently modified or freed. If path is a null pointer or points to an empty string, or if the string pointed to by path consists entirely of the ‘/’ character, the returned pointer may point to constant data that cannot be modified.

RETURN VALUE

The basename () function shall return a pointer to the final component of path.

The basename () function shall always be successful and no return value is reserved to indicate an error.

ERRORS

No errors are defined.

The following sections are informative.

EXAMPLES

Using basename()

The following program fragment returns a pointer to the value lib, which is the base name of /usr/lib.

#include <libgen.h>
...
char name[] = "/usr/lib";
char *base;


base = basename(name);
...

Sample Input and Output Strings for the basename() and dirname() Functions and the basename and dirname Utilities

basename() and dirname Functions path Argument	String Returned by basename()	String Returned by dirname()	basename and dirname Utilities string Operand	Output Written by basename Utility	Output Written by dirname Utility
usr	usr	.	usr	usr	.
usr/	usr	.	usr/	usr	.
	.	.	empty string	. or empty string	.
/	/	/	/	/	/
//	/ or // (see note 1)	/ or // (see note 1)	//	/ or // (see note 1)	/ or // (see note 1)
///	/	/ or ///	///	/	/ or ///
/usr/	usr	/	/usr/	usr	/
/usr/lib	lib	/usr	/usr/lib	lib	/usr
//usr//lib//	lib	//usr or /usr (see note 1)	//usr//lib//	lib	//usr or /usr (see note 1)
/home//dwc//test	test	/home//dwc or /home/dwc	/home//dwc//test	test	/home//dwc or /home/dwc
/home/.././test Ta test"	/home/../. or /home/..	/home/.././test	test	/home/../. or /home/..
/home/dwc/.	.	/home/dwc	/home/dwc/.	.	/home/dwc

Note

Whether leading // can be converted to / depends on the implementation-defined behavior of // (see XBD 4.16 Pathname Resolution ; although the basename () and dirname () functions, and basename and dirname utilities, do not themselves perform pathname resolution, their results can be passed to a function or utility which does).

APPLICATION USAGE

Note that in some circumstances (in particular, when the returned string is required to be "/" or "." ), the returned pointer might point into constant data. Therefore, if the application needs to modify the returned data, it should be copied first.

RATIONALE

Earlier versions of this standard seemed to allow thread-safe and non-thread-safe implementations of basename () and dirname(3), but did not allow implementations to return a null pointer and require that errno be set when that happened. The standard now requires thread-safe behavior for both of these functions and clearly states that they are always successful.

FUTURE DIRECTIONS

None.

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.

Issue 6

In the DESCRIPTION, the note about reentrancy is expanded to cover thread-safety.

IEEE Std 1003.1-2001 (“POSIX.1”)/Cor 2-2004, item XSH/TC2/D6/20 is applied, changing the DESCRIPTION to make it clear that the string referenced is the string pointed to by path.

Issue 7

Austin Group Interpretation 1003.1-2001 #156 is applied.

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0041 [75] is applied.

POSIX.1-2008, Technical Corrigendum 2, XSH/TC2-2008/0047 [656], XSH/TC2-2008/0048 [928], and XSH/TC2-2008/0049 [612] are applied.

Issue 8

Austin Group Defects 1064 and 1358 are applied, requiring basename () to be thread-safe and allowing it to return a pointer to constant data under certain conditions.

Austin Group Defect 1073 is applied, changing the EXAMPLES section.

Austin Group Defect 1396 is applied, changing the EXAMPLES section.

End of informative text.