expands all symbolic links and resolves references
and extra '/'
characters in the null-terminated string named by
to produce a canonicalized absolute pathname.
The resulting pathname is stored as a null-terminated string,
up to a maximum of
in the buffer pointed to by
The resulting path will have no symbolic link,
is specified as NULL, then
to allocate a buffer of up to
bytes to hold the resolved pathname,
and returns a pointer to this buffer.
The caller should deallocate this buffer using
If there is no error,
returns a pointer to the
Otherwise it returns a NULL pointer, and the contents
of the array
are undefined, and
is set to indicate the error.
Read or search permission was denied for a component of the path prefix.
(In libc5 this would just cause a segfault.)
But, see NOTES below.
An I/O error occurred while reading from the file system.
Too many symbolic links were encountered in translating the pathname.
A component of a pathname exceeded
characters, or an entire pathname exceeded
The named file does not exist.
A component of the path prefix is not a directory.
On Linux this function appeared in libc 4.5.21.
POSIX.1-2001 says that the behavior if
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
(found in <sys/param.h>).
as found in <limits.h> or provided by the
A typical source fragment would be
The 4.4BSD, Linux and SUSv2 versions always return an absolute
Solaris may return a relative pathname when the
argument is relative.
The prototype of
is given in <unistd.h> in libc4 and libc5,
but in <stdlib.h> everywhere else.
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,
According to POSIX.1-2001 a buffer of size
need not be a defined constant, and may have to be obtained using
does not really help, since, on the one hand POSIX warns that
the result of
may be huge and unsuitable for mallocing memory,
and on the other hand
may return -1 to signify that
is not bounded.
resolved_path == NULL
feature, not standardized in POSIX.1-2001,
but standardized in POSIX.1-2008, allows this design problem to be avoided.
The libc4 and libc5 implementation contains a buffer overflow
(fixed in libc-5.4.13).
Thus, set-user-ID programs like
need a private version.