get_current_dir_name − get current working
*getcwd(char *buf, size_t
Macro Requirements for glibc (see
Since glibc 2.12:
(_XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED)
!(_POSIX_C_SOURCE >= 200809L ||
_XOPEN_SOURCE >= 700)
Before glibc 2.12:
_XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
return a null-terminated string containing an absolute
pathname that is the current working directory of the
calling process. The pathname is returned as the function
result and via the argument buf, if present.
If the current
directory is not below the root directory of the current
process (e.g., because the process set a new filesystem root
using chroot(2) without changing its current
directory into the new root), then, since Linux 2.6.36, the
returned path will be prefixed with the string
"(unreachable)". Such behavior can also be caused
by an unprivileged user by changing the current directory
into another mount namespace. When dealing with paths from
untrusted sources, callers of these functions should
consider checking whether the returned path starts with
’/’ or ’(’ to avoid misinterpreting
an unreachable path as a relative path.
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 length
of the absolute pathname of the current working directory,
including the terminating null byte, exceeds size
bytes, NULL is returned, and errno is set to
ERANGE; an application should check for this error,
and allocate a larger buffer if necessary.
As an extension
to the POSIX.1-2001 standard, glibc’s getcwd()
allocates the buffer dynamically using malloc(3) if
buf is NULL. In this case, the allocated buffer has
the length size unless size is zero, when
buf is allocated as big as necessary. The caller
should free(3) the returned buffer.
will malloc(3) an array big enough to hold the
absolute pathname of the current working directory. If the
environment variable PWD is set, and its value is
correct, then that value will be returned. The caller should
free(3) the returned buffer.
does not malloc(3) any memory. The buf
argument should be a pointer to an array at least
PATH_MAX bytes long. If the length of the absolute
pathname of the current working directory, including the
terminating null byte, exceeds PATH_MAX bytes, NULL
is returned, and errno is set to ENAMETOOLONG.
(Note that on some systems, PATH_MAX may not be a
compile-time constant; furthermore, its value may depend on
the filesystem, see pathconf(3).) For portability and
security reasons, use of getwd() is deprecated.
these functions return a pointer to a string containing the
pathname of the current working directory. In the case
getcwd() and getwd() this is the same value as
these functions return NULL, and errno is set to
indicate the error. The contents of the array pointed to by
buf are 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
getwd(): buf is NULL.
getwd(): The size of the
null-terminated absolute pathname string exceeds
Out of memory.
The current working directory has been unlinked.
The size argument is less than the length of the
absolute pathname of the working directory, including the
terminating null byte. You need to allocate a bigger array
and try again.
explanation of the terms used in this section, see
conforms to POSIX.1-2001. Note however that POSIX.1-2001
leaves the behavior of getcwd() unspecified if
buf is NULL.
is present in POSIX.1-2001, but marked LEGACY. POSIX.1-2008
removes the specification of getwd(). Use
getcwd() instead. POSIX.1-2001 does not define any
errors for getwd().
is a GNU extension.
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
filesystem are missing, a generic implementation is called.
Only in that case can these calls fail under Linux with
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.
fchdir(2), open(2), unlink(2),
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