getcwd, get_current_dir_name, getwd — Get current working directory
#include <unistd.h>
char
*getcwd( |
char * | buf, |
size_t | size) ; |
#define _BSD_SOURCE /* Or: #define _XOPEN_SOURCE 500 */ #include <unistd.h>
char
*getwd( |
char * | buf) ; |
#define _GNU_SOURCE #include <unistd.h>
char
*get_current_dir_name( |
void) ; |
The getcwd
() function copies
an absolute pathname of the current working directory to the
array pointed to by buf
, which is of length
size
.
If the current absolute pathname would require a buffer
longer than size
elements, NULL is returned, and errno
is set to ERANGE; an application should check for
this error, and allocate a larger buffer if necessary.
If buf
is NULL,
the behaviour of getcwd
() is
undefined.
As an extension to the POSIX.1-2001 standard, Linux
(libc4, libc5, glibc) getcwd
()
allocates the buffer dynamically using malloc(3) if buf
is NULL on call. In this
case, the allocated buffer has the length size
unless size
is zero, when buf
is allocated as big as
necessary. It is possible (and, indeed, advisable) to
free(3) the buffers if they
have been obtained this way.
get_current_dir_name
(), will
malloc(3) an array big
enough to hold the current directory name. If the environment
variable PWD
is set, and its
value is correct, then that value will be returned.
getwd
(), does not malloc(3) any memory. The
buf
argument should
be a pointer to an array at least PATH_MAX
bytes long. getwd
() does only return the first
PATH_MAX
bytes of the actual
pathname. Note that PATH_MAX
need not be a compile-time constant; it may depend on the
filesystem and may even be unlimited. For portability and
security reasons, use of getwd
() is deprecated.
NULL on failure with errno
set accordingly, and buf
on success. The contents of
the array pointed to by buf
is undefined on error.
Permission to read or search a component of the filename was denied.
buf
points
to a bad address.
The size
argument is zero and buf
is not a null
pointer.
The current working directory has been unlinked.
The size
argument is less than the length of the working
directory name. You need to allocate a bigger array and
try again.
Under Linux, the function getcwd
() is a system call (since 2.1.92).
On older systems it would query /proc/self/cwd
. If both system call and
proc file system are missing, a generic implementation is
called. Only in that case can these calls fail under Linux
with EACCES.
These functions are often used to save the location of the current working directory for the purpose of returning to it later. Opening the current directory (".") and calling fchdir(2) to return is usually a faster and more reliable alternative when sufficiently many file descriptors are available, especially on platforms other than Linux.
getcwd
() conforms to
POSIX.1-2001. getwd
() is
present in POSIX.1-2001, but marked LEGACY. get_current_dir_name
() is a GNU
extension.
chdir(2), fchdir(2), open(2), unlink(2), free(3), malloc(3), feature_test_macros(7)
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