getcwd, get_current_dir_name, getwd - Get current working
char *getcwd(char *buf, size_t size));
char *getwd(char *buf));
The getcwd() function copies the absolute pathname of the
current working 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 application should check for this error,
and allocate a larger buffer if necessary.
As an extension to the POSIX.1 standard, 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 less than zero, when buf is allocated as
big as necessary. It is possible (and, indeed, advisable)
to free() the buffers if they have been obtained this way.
get_current_dir_name, which is only prototyped if __USE_GNU
is defined, will malloc(3) an array big enough to hold the
current directory name. If the environment variable PWD is
set, and its value is correct, then that value will be
getwd, which is only prototyped if __USE_BSD 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
NULL on failure (for example, if the current directory is
not readable), with errno set accordingly, and buf on suc-
chdir(2), free(3), malloc(3).