Manpage of GETCWD

GETCWD

Section: Linux Programmer's Manual (3)
Updated: 2016-03-15
Index
 

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)):

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 versions <= 2.19: */ _BSD_SOURCE
Before glibc 2.12: _BSD_SOURCE || _XOPEN_SOURCE >= 500
 

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.

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.

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 sizebytes, NULL is returned, and errnois 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 bufis NULL. In this case, the allocated buffer has the length sizeunless sizeis zero, when bufis 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 PWDis 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 bufargument should be a pointer to an array at least PATH_MAXbytes long. If the length of the absolute pathname of the current working directory, including the terminating null byte, exceeds PATH_MAXbytes, NULL is returned, and errnois set to ENAMETOOLONG. (Note that on some systems, PATH_MAXmay 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.  

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 errnois set to indicate the error. The contents of the array pointed to by bufare undefined on error.  

ERRORS

EACCES
Permission to read or search a component of the filename was denied.
EFAULT
bufpoints to a bad address.
EINVAL
The sizeargument is zero and bufis not a null pointer.
EINVAL
getwd(): bufis NULL.
ENAMETOOLONG
getwd(): The size of the null-terminated absolute pathname string exceeds PATH_MAXbytes.
ENOMEM
Out of memory.
ENOENT
The current working directory has been unlinked.
ERANGE
The sizeargument 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.
 

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).
InterfaceAttributeValue
getcwd(), getwd() Thread safetyMT-Safe
get_current_dir_name() Thread safetyMT-Safe env
 

CONFORMING TO

getcwd() conforms to POSIX.1-2001. Note however that POSIX.1-2001 leaves the behavior of getcwd() unspecified if bufis 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 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.  

SEE ALSO

pwd(1), chdir(2), fchdir(2), open(2), unlink(2), free(3), malloc(3)


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
ATTRIBUTES
CONFORMING TO
NOTES
SEE ALSO

This document was created by man2html, using the manual pages.
Time: 22:27:58 GMT, June 20, 2016 Click Here!