Each process has associated with it a directory, called its current working directory or simply working directory, that is used in the resolution of relative file names (see section File Name Resolution).
When you log in and begin a new session, your working directory is
initially set to the home directory associated with your login account
in the system user database. You can find any user's home directory
using the getpwuid
or getpwnam
functions; see section User Database.
Users can change the working directory using shell commands like
cd
. The functions described in this section are the primitives
used by those commands and by other programs for examining and changing
the working directory.
Prototypes for these functions are declared in the header file `unistd.h'.
getcwd
function returns an absolute file name representing
the current working directory, storing it in the character array
buffer that you provide. The size argument is how you tell
the system the allocation size of buffer.
The GNU library version of this function also permits you to specify a
null pointer for the buffer argument. Then getcwd
allocates a buffer automatically, as with malloc
(see section Unconstrained Allocation). If the size is greater than
zero, then the buffer is that large; otherwise, the buffer is as large
as necessary to hold the result.
The return value is buffer on success and a null pointer on failure.
The following errno
error conditions are defined for this function:
EINVAL
ERANGE
EACCES
You could implement the behavior of GNU's getcwd (NULL, 0)
using only the standard behavior of getcwd
:
char * gnu_getcwd () { size_t size = 100; while (1) { char *buffer = (char *) xmalloc (size); if (getcwd (buffer, size) == buffer) return buffer; free (buffer); if (errno != ERANGE) return 0; size *= 2; } }
See section Examples of malloc
, for information about xmalloc
, which is
not a library function but is a customary name used in most GNU
software.
getcwd
, but has no way to specify the size of
the buffer. The GNU library provides getwd
only
for backwards compatibility with BSD.
The buffer argument should be a pointer to an array at least
PATH_MAX
bytes long (see section Limits on File System Capacity). In the GNU
system there is no limit to the size of a file name, so this is not
necessarily enough space to contain the directory name. That is why
this function is deprecated.
get_current_dir_name
function is bascially equivalent to
getcwd (NULL, 0)
. The only difference is that the value of
the PWD
variable is returned if this value is correct. This is a
subtle difference which is visible if the path described by the
PWD
value is using one or more symbol links in which case the
value returned by getcwd
can resolve the symbol links and
therefore yield a different result.
This function is a GNU extension.
The normal, successful return value from chdir
is 0
. A
value of -1
is returned to indicate an error. The errno
error conditions defined for this function are the usual file name
syntax errors (see section File Name Errors), plus ENOTDIR
if the
file filename is not a directory.
The normal, successful return value from fchdir
is 0
. A
value of -1
is returned to indicate an error. The following
errno
error conditions are defined for this function:
EACCES
dirname
.
EBADF
ENOTDIR
EINTR
EIO
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