The getcwd() function copies an absolute pathname of the current working
directory to the array pointed to by buf, which is of length
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
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 possible (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
directory 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
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.