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.
- EACCES
- Read or search permission was denied for a component of the path
prefix.
- EINVAL
- path is NULL. (In glibc versions before 2.3, this error is also
returned if resolved_path is NULL.)
- EIO
- An I/O error occurred while reading from the filesystem.
- ELOOP
- Too many symbolic links were encountered in translating the pathname.
- ENAMETOOLONG
- A component of a pathname exceeded NAME_MAX characters, or an
entire pathname exceeded PATH_MAX characters.
- ENOENT
- The named file does not exist.
- ENOMEM
- Out of memory.
- ENOTDIR
- 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.
realpath(1),
readlink(2),
canonicalize_file_name(3),
getcwd(3),
pathconf(3),
sysconf(3)