NAME
getcwd - get the pathname of the current working directory
SYNOPSIS
#include <unistd.h>
char *getcwd(char *buf, size_t size);
DESCRIPTION
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 copied to the array shall contain no components that are
symbolic links. 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.
RETURN VALUE
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.
ERRORS
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 pathname +1.
The getcwd() function may fail if:
EACCES Read or search permission was denied for a component of the
pathname.
ENOMEM Insufficient storage space is available.
The following sections are informative.
EXAMPLES
Determining the Absolute Pathname of the Current Working Directory
The following example returns a pointer to an array that holds the
absolute pathname of the current working directory. The pointer is
returned in the ptr variable, which points to the buf array where the
pathname is stored.
#include <stdlib.h>
#include <unistd.h>
...
long size;
char *buf;
char *ptr;
size = pathconf(".", _PC_PATH_MAX);
if ((buf = (char *)malloc((size_t)size)) != NULL)
ptr = getcwd(buf, (size_t)size);
...
APPLICATION USAGE
None.
RATIONALE
Since the maximum pathname length is arbitrary unless {PATH_MAX} is
defined, an application generally cannot supply a buf with size
{{PATH_MAX}+1}.
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. Also,
malloc() and free() are used nowhere else in this volume of
IEEE Std 1003.1-2001. Finally, getcwd() is taken from the SVID where it
has the two arguments used in this volume of IEEE Std 1003.1-2001.
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.
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 writer that getcwd() can fail for
reasons beyond the control of the application writer 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 IEEE Std 1003.1-2001
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.
FUTURE DIRECTIONS
None.
SEE ALSO
malloc() , the Base Definitions volume of IEEE Std 1003.1-2001,
<unistd.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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 .