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GETCWD(3) Linux Programmer's Manual GETCWD(3)
NAME
getcwd, getwd, get_current_dir_name - Get current working directory
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)):
getcwd(): _BSD_SOURCE || _XOPEN_SOURCE >= 500
get_current_dir_name(): _GNU_SOURCE
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 work‐
ing directory to the array pointed to by buf, which is of length size.
If the length of the absolute pathname of the current working direc‐
tory, 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, Linux (libc4, libc5,
glibc) 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 ter‐
minating 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
file system, see pathconf(3).) For portability and security reasons,
use of getwd() is deprecated.
RETURN VALUE
On success, 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 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.
ERRORS
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.
ERANGE The size argument is less than the length of the absolute path‐
name of the working directory, including the terminating null
byte. You need to allocate a bigger array and try again.
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.
NOTES
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.
SEE ALSO
chdir(2), fchdir(2), open(2), unlink(2), free(3), malloc(3)
COLOPHON
This page is part of release 3.24 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
GNU 2009-03-31 GETCWD(3) |
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发表于 2010-10-29 09:53
