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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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GETCWD(3P) POSIX Programmer's Manual GETCWD(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.
getcwd — get the pathname of the current working directory
#include <unistd.h>
char *getcwd(char *buf, size_t size);
The getcwd() function shall place an absolute pathname of the
current working directory in the array pointed to by buf, and
return buf. The pathname shall contain no components that are dot
or dot-dot, or are symbolic links.
If there are multiple pathnames that getcwd() could place in the
array pointed to by buf, one beginning with a single <slash>
character and one or more beginning with two <slash> characters,
then getcwd() shall place the pathname beginning with a single
<slash> character in the array. The pathname shall not contain any
unnecessary <slash> characters after the leading one or two
<slash> characters.
The size argument is the size in bytes of the character array
pointed to by the buf argument. If buf is a null pointer, the
behavior of getcwd() is unspecified.
Upon successful completion, getcwd() shall return the buf
argument. Otherwise, getcwd() shall return a null pointer and set
errno to indicate the error. The contents of the array pointed to
by buf are then undefined.
The getcwd() function shall fail if:
EINVAL The size argument is 0.
ERANGE The size argument is greater than 0, but is smaller than
the length of the string +1.
The getcwd() function may fail if:
EACCES 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.
ENOMEM Insufficient storage space is available.
The following sections are informative.
The following example uses {PATH_MAX} as the initial buffer size
(unless it is indeterminate or very large), and calls getcwd()
with progressively larger buffers until it does not give an
[ERANGE] error.
#include <stdlib.h>
#include <errno.h>
#include <unistd.h>
...
long path_max;
size_t size;
char *buf;
char *ptr;
path_max = pathconf(".", _PC_PATH_MAX);
if (path_max == -1)
size = 1024;
else if (path_max > 10240)
size = 10240;
else
size = path_max;
for (buf = ptr = NULL; ptr == NULL; size *= 2)
{
if ((buf = realloc(buf, size)) == NULL)
{
... handle error ...
}
ptr = getcwd(buf, size);
if (ptr == NULL && errno != ERANGE)
{
... handle error ...
}
}
...
free (buf);
If the pathname obtained from getcwd() is longer than {PATH_MAX}
bytes, it could produce an [ENAMETOOLONG] error if passed to
chdir(). Therefore, in order to return to that directory it may
be necessary to break the pathname into sections shorter than
{PATH_MAX} bytes and call chdir() on each section in turn (the
first section being an absolute pathname and subsequent sections
being relative pathnames). A simpler way to handle saving and
restoring the working directory when it may be deeper than
{PATH_MAX} bytes in the file hierarchy is to use a file descriptor
and fchdir(), rather than getcwd() and chdir(). However, the two
methods do have some differences. The fchdir() approach causes the
program to restore a working directory even if it has been renamed
in the meantime, whereas the chdir() approach restores to a
directory with the same name as the original, even if the
directories were renamed in the meantime. Since the fchdir()
approach does not access parent directories, it can succeed when
getcwd() would fail due to permissions problems. In applications
conforming to earlier versions of this standard, it was not
possible to use the fchdir() approach when the working directory
is searchable but not readable, as the only way to open a
directory was with O_RDONLY, whereas the getcwd() approach can
succeed in this case.
Having getcwd() take no arguments and instead use the malloc()
function to produce space for the returned argument was
considered. The advantage is that getcwd() knows how big the
working directory pathname is and can allocate an appropriate
amount of space. But the programmer would have to use the free()
function to free the resulting object, or each use of getcwd()
would further reduce the available memory. Finally, getcwd() is
taken from the SVID where it has the two arguments used in this
volume of POSIX.1‐2017.
The older function getwd() was rejected for use in this context
because it had only a buffer argument and no size argument, and
thus had no way to prevent overwriting the buffer, except to
depend on the programmer to provide a large enough buffer.
On some implementations, if buf is a null pointer, getcwd() may
obtain size bytes of memory using malloc(). In this case, the
pointer returned by getcwd() may be used as the argument in a
subsequent call to free(). Invoking getcwd() with buf as a null
pointer is not recommended in conforming applications.
Earlier implementations of getcwd() sometimes generated pathnames
like "../../../subdirname" internally, using them to explore the
path of ancestor directories back to the root. If one of these
internal pathnames exceeded {PATH_MAX} in length, the
implementation could fail with errno set to [ENAMETOOLONG]. This
is no longer allowed.
If a program is operating in a directory where some (grand)parent
directory does not permit reading, getcwd() may fail, as in most
implementations it must read the directory to determine the name
of the file. This can occur if search, but not read, permission is
granted in an intermediate directory, or if the program is placed
in that directory by some more privileged process (for example,
login). Including the [EACCES] error condition makes the reporting
of the error consistent and warns the application developer that
getcwd() can fail for reasons beyond the control of the
application developer or user. Some implementations can avoid this
occurrence (for example, by implementing getcwd() using pwd, where
pwd is a set-user-root process), thus the error was made optional.
Since this volume of POSIX.1‐2017 permits the addition of other
errors, this would be a common addition and yet one that
applications could not be expected to deal with without this
addition.
None.
malloc(3p)
The Base Definitions volume of POSIX.1‐2017, unistd.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 GETCWD(3P)
Pages that refer to this page: unistd.h(0p), pwd(1p), chdir(3p), realpath(3p)
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HTML rendering created 2025-02-02 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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