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### 14.1 Working Directory

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 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 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`.

— Function: char * getcwd (char *buffer, size_t size)

> The `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 C 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 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`
>   The size argument is zero and buffer is not a null pointer.
> `ERANGE`
>   The size argument is less than the length of the working directory name. You need to allocate a bigger array and try again.
> `EACCES`
>   Permission to read or search a component of the file name was denied.

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 Malloc Examples, for information about `xmalloc`, which is not a library function but is a customary name used in most GNU software.

— Deprecated Function: char * getwd (char *buffer)

> This is similar to `getcwd`, but has no way to specify the size of the buffer. The GNU C 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 Limits for Files). On GNU/Hurd systems 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.

— Function: char * get_current_dir_name (void)

> This `get_current_dir_name` function is basically 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.

— Function: int chdir (const char *filename)

> This function is used to set the process's working directory to filename.

> 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 File Name Errors), plus `ENOTDIR` if the file filename is not a directory.

— Function: int fchdir (int filedes)

> This function is used to set the process's working directory to directory associated with the file descriptor filedes.

> 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`
>   Read permission is denied for the directory named by `dirname`.
> `EBADF`
>   The filedes argument is not a valid file descriptor.
> `ENOTDIR`
>   The file descriptor filedes is not associated with a directory.
> `EINTR`
>   The function call was interrupt by a signal.
> `EIO`
>   An I/O error occurred.