realpath - return the canonicalized absolute pathname
#include <limits.h>
#include <stdlib.h>
char *realpath(const char *path, char *resolved_path);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
realpath():
_XOPEN_SOURCE >= 500 || /* Glibc since 2.19: */ _DEFAULT_SOURCE || /* Glibc versions <= 2.19: */ _BSD_SOURCE
realpath() expands all symbolic links and resolves
references to /./
, /../
and extra '/' characters in
the null-terminated string named by path
to produce a
canonicalized absolute pathname. The resulting pathname is stored as a
null-terminated string, up to a maximum of PATH_MAX
bytes, in the buffer pointed to by resolved_path
. The resulting
path will have no symbolic link, /./
or /../
components.
If resolved_path
is specified as NULL, then
realpath() uses malloc(3) to allocate
a buffer of up to PATH_MAX bytes to hold the resolved
pathname, and returns a pointer to this buffer. The caller should
deallocate this buffer using free(3).
If there is no error, realpath() returns a pointer
to the resolved_path
.
Otherwise, it returns NULL, the contents of the array
resolved_path
are undefined, and errno
is set to
indicate the error.
Read or search permission was denied for a component of the path prefix.
path
is NULL. (In glibc versions before 2.3, this error is
also returned if resolved_path
is NULL.)
An I/O error occurred while reading from the filesystem.
Too many symbolic links were encountered in translating the pathname.
A component of a pathname exceeded NAME_MAX characters, or an entire pathname exceeded PATH_MAX characters.
The named file does not exist.
Out of memory.
A component of the path prefix is not a directory.
For an explanation of the terms used in this section, see attributes(7).
Interface | Attribute | Value |
realpath() | Thread safety | MT-Safe |
4.4BSD, POSIX.1-2001.
POSIX.1-2001 says that the behavior if resolved_path
is NULL
is implementation-defined. POSIX.1-2008 specifies the behavior described
in this page.
In 4.4BSD and Solaris, the limit on the pathname length is
MAXPATHLEN (found in <sys/param.h>
).
SUSv2 prescribes PATH_MAX and
NAME_MAX, as found in <limits.h>
or
provided by the pathconf(3) function. A typical source
fragment would be
#ifdef PATH_MAX
path_max = PATH_MAX;
#else
path_max = pathconf(path, _PC_PATH_MAX);
if (path_max <= 0)
path_max = 4096;
#endif
(But see the BUGS section.)
If the call fails with either EACCES or
ENOENT and resolved_path
is not NULL, then the
prefix of path
that is not readable or does not exist is
returned in resolved_path
.
The POSIX.1-2001 standard version of this function is broken by
design, since it is impossible to determine a suitable size for the
output buffer, resolved_path
. According to POSIX.1-2001 a
buffer of size PATH_MAX suffices, but
PATH_MAX need not be a defined constant, and may have
to be obtained using pathconf(3). And asking
pathconf(3) does not really help, since, on the one
hand POSIX warns that the result of pathconf(3) may be
huge and unsuitable for mallocing memory, and on the other hand
pathconf(3) may return -1 to signify that
PATH_MAX is not bounded. The resolved_path ==
NULL feature, not standardized in POSIX.1-2001, but standardized in
POSIX.1-2008, allows this design problem to be avoided.
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