получить текущий рабочий каталог (get current working directory)
Имя (Name)
getcwd, getwd, get_current_dir_name - get current working
directory
Синопсис (Synopsis)
#include <unistd.h>
char *getcwd(char *buf, size_t size);
char *getwd(char *buf);
char *get_current_dir_name(void);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
get_current_dir_name():
_GNU_SOURCE
getwd():
Since glibc 2.12:
(_XOPEN_SOURCE >= 500) && ! (_POSIX_C_SOURCE >= 200809L)
|| /* Glibc since 2.19: */ _DEFAULT_SOURCE
|| /* Glibc <= 2.19: */ _BSD_SOURCE
Before glibc 2.12:
_BSD_SOURCE || _XOPEN_SOURCE >= 500
Описание (Description)
These functions 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.
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 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.
get_current_dir_name() 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.
getwd() 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.
Возвращаемое значение (Return value)
On success, these functions return a pointer to a string
containing the pathname of the current working directory. In the
case of getcwd() and getwd() this is the same value as buf.
On failure, 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.
Ошибки (Error)
EACCES Permission to read or search a component of the filename
was denied.
EFAULT buf points to a bad address.
EINVAL The size argument is zero and buf is not a null pointer.
EINVAL getwd(): buf is NULL.
ENAMETOOLONG
getwd(): The size of the null-terminated absolute pathname
string exceeds PATH_MAX bytes.
ENOENT The current working directory has been unlinked.
ENOMEM Out of memory.
ERANGE 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.
Атрибуты (Attributes)
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────┬───────────────┬─────────────┐
│Interface │ Attribute │ Value │
├──────────────────────────────────┼───────────────┼─────────────┤
│getcwd(), getwd() │ Thread safety │ MT-Safe │
├──────────────────────────────────┼───────────────┼─────────────┤
│get_current_dir_name() │ Thread safety │ MT-Safe env │
└──────────────────────────────────┴───────────────┴─────────────┘
Стандарты (Conforming to)
getcwd() conforms to POSIX.1-2001. Note however that
POSIX.1-2001 leaves the behavior of getcwd() unspecified if buf
is NULL.
getwd() 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().
get_current_dir_name() is a GNU extension.
Примечание (Note)
Under Linux, these functions make use of the getcwd() system call
(available since Linux 2.1.92). On older systems they 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 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.
C library/kernel differences
On Linux, the kernel provides a getcwd() system call, which the
functions described in this page will use if possible. The
system call takes the same arguments as the library function of
the same name, but is limited to returning at most PATH_MAX
bytes. (Before Linux 3.12, the limit on the size of the returned
pathname was the system page size. On many architectures,
PATH_MAX and the system page size are both 4096 bytes, but a few
architectures have a larger page size.) If the length of the
pathname of the current working directory exceeds this limit,
then the system call fails with the error ENAMETOOLONG. In this
case, the library functions fall back to a (slower) alternative
implementation that returns the full pathname.
Following a change in Linux 2.6.36, the pathname returned by the
getcwd() system call will be prefixed with the string
"(unreachable)" 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). Such behavior can also be caused
by an unprivileged user by changing the current directory into
another mount namespace. When dealing with pathname from
untrusted sources, callers of the functions described in this
page should consider checking whether the returned pathname
starts with '/' or '(' to avoid misinterpreting an unreachable
path as a relative pathname.
Ошибки (баги) (Bugs)
Since the Linux 2.6.36 change that added "(unreachable)" in the
circumstances described above, the glibc implementation of
getcwd() has failed to conform to POSIX and returned a relative
pathname when the API contract requires an absolute pathname.
With glibc 2.27 onwards this is corrected; calling getcwd() from
such a pathname will now result in failure with ENOENT.
Смотри также (See also)
pwd(1), chdir(2), fchdir(2), open(2), unlink(2), free(3),
malloc(3)
