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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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REALPATH(3P) POSIX Programmer's Manual REALPATH(3P)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
realpath — resolve a pathname
#include <stdlib.h>
char *realpath(const char *restrict file_name,
char *restrict resolved_name);
The realpath() function shall derive, from the pathname pointed to
by file_name, an absolute pathname that resolves to the same
directory entry, whose resolution does not involve '.', '..', or
symbolic links. If resolved_name is a null pointer, the generated
pathname shall be stored as a null-terminated string in a buffer
allocated as if by a call to malloc(). Otherwise, if {PATH_MAX}
is defined as a constant in the <limits.h> header, then the
generated pathname shall be stored as a null-terminated string, up
to a maximum of {PATH_MAX} bytes, in the buffer pointed to by
resolved_name.
If resolved_name is not a null pointer and {PATH_MAX} is not
defined as a constant in the <limits.h> header, the behavior is
undefined.
Upon successful completion, realpath() shall return a pointer to
the buffer containing the resolved name. Otherwise, realpath()
shall return a null pointer and set errno to indicate the error.
If the resolved_name argument is a null pointer, the pointer
returned by realpath() can be passed to free().
If the resolved_name argument is not a null pointer and the
realpath() function fails, the contents of the buffer pointed to
by resolved_name are undefined.
The realpath() function shall fail if:
EACCES Search permission was denied for a component of the path
prefix of file_name.
EINVAL The file_name argument is a null pointer.
EIO An error occurred while reading from the file system.
ELOOP A loop exists in symbolic links encountered during
resolution of the file_name argument.
ENAMETOOLONG
The length of a component of a pathname is longer than
{NAME_MAX}.
ENOENT A component of file_name does not name an existing file or
file_name points to an empty string.
ENOTDIR
A component of the path prefix names an existing file that
is neither a directory nor a symbolic link to a directory,
or the file_name argument contains at least one non-<slash>
character and ends with one or more trailing <slash>
characters and the last pathname component names an
existing file that is neither a directory nor a symbolic
link to a directory.
The realpath() function may fail if:
EACCES The file_name argument does not begin with a <slash> and
none of the symbolic links (if any) processed during
pathname resolution of file_name had contents that began
with a <slash>, and either search permission was denied for
the current directory or read or search permission was
denied for a directory above the current directory in the
file hierarchy.
ELOOP More than {SYMLOOP_MAX} symbolic links were encountered
during resolution of the file_name argument.
ENAMETOOLONG
The length of a pathname exceeds {PATH_MAX}, or pathname
resolution of a symbolic link produced an intermediate
result with a length that exceeds {PATH_MAX}.
ENOMEM Insufficient storage space is available.
The following sections are informative.
Generating an Absolute Pathname
The following example generates an absolute pathname for the file
identified by the symlinkpath argument. The generated pathname is
stored in the buffer pointed to by actualpath.
#include <stdlib.h>
...
char *symlinkpath = "/tmp/symlink/file";
char *actualpath;
actualpath = realpath(symlinkpath, NULL);
if (actualpath != NULL)
{
... use actualpath ...
free(actualpath);
}
else
{
... handle error ...
}
For functions that allocate memory as if by malloc(), the
application should release such memory when it is no longer
required by a call to free(). For realpath(), this is the return
value.
Since realpath() has no length argument, if {PATH_MAX} is not
defined as a constant in <limits.h>, applications have no way of
determining how large a buffer they need to allocate for it to be
safe to pass to realpath(). A {PATH_MAX} value obtained from a
prior pathconf() call is out-of-date by the time realpath() is
called. Hence the only reliable way to use realpath() when
{PATH_MAX} is not defined in <limits.h> is to pass a null pointer
for resolved_name so that realpath() will allocate a buffer of the
necessary size.
None.
fpathconf(3p), free(3p), getcwd(3p), sysconf(3p)
The Base Definitions volume of POSIX.1‐2017, limits.h(0p),
stdlib.h(0p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics Engineers,
Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard,
the original IEEE and The Open Group Standard is the referee
document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page
are most likely to have been introduced during the conversion of
the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 REALPATH(3P)
Pages that refer to this page: stdlib.h(0p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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