GETCWD(3) Linux Programmer's Manual GETCWD(3)
NAME
getcwd, get_current_dir_name, getwd - Get current working directory
SYNOPSIS
#include<unistd.h>
char*getcwd(char*buf,size_t size);
char*get_current_dir_name(void);
char*getwd(char*buf);
DESCRIPTION
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 current absolute path name would require a buffer longer than
size elements, NULL is returned, and errno is set to ERANGE; an appli-
cation 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 standard, Linux (libc4, libc5, glibc)
getcwd() allocates the buffer dynamically using malloc() 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 possi-
ble (and, indeed, advisable) to free() the buffers if they have been
obtained this way.
get_current_dir_name, which is only prototyped if _GNU_SOURCE is
defined, will malloc(3) an array big enough to hold the current direc-
tory name. If the environment variable PWD is set, and its value is
correct, then that value will be returned.
getwd, which is only prototyped if _BSD_SOURCE or
_XOPEN_SOURCE_EXTENDED is defined, will 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.
RETURNVALUE
NULL on failure with errno set accordingly, and buf on success. The
contents of the array pointed to by buf is undefined on error.
ERRORS
EACCES Permission to read or search a component of the file name was
denied.
EFAULT buf points to a bad address.
EINVAL The size argument is zero and buf is not a null pointer.
ENOENT The current working directory has been unlinked.
ERANGE The size argument is less than the length of the working direc-
tory name. You need to allocate a bigger array and try again.
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.
CONFORMINGTO
POSIX.1
SEEALSO
chdir(2), fchdir(2), open(2), unlink(2), free(3), malloc(3)
GNU 2002-04-22 GETCWD(3)
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