Originální popis anglicky:
getcwd - get the pathname of the current working directory
Návod, kniha: POSIX Programmer's Manual
#include <unistd.h>
char *getcwd(char *
buf, size_t
size);
The
getcwd() function shall place an absolute pathname of the current
working directory in the array pointed to by
buf, and return
buf. The pathname copied to the array shall contain no components that
are symbolic links. The
size argument is the size in bytes of the
character array pointed to by the
buf argument. If
buf is a null
pointer, the behavior of
getcwd() is unspecified.
Upon successful completion,
getcwd() shall return the
buf
argument. Otherwise,
getcwd() shall return a null pointer and set
errno to indicate the error. The contents of the array pointed to by
buf are then undefined.
The
getcwd() function shall fail if:
- EINVAL
- The size argument is 0.
- ERANGE
- The size argument is greater than 0, but is smaller
than the length of the pathname +1.
The
getcwd() function may fail if:
- EACCES
- Read or search permission was denied for a component of the
pathname.
- ENOMEM
- Insufficient storage space is available.
The following sections are informative.
The following example returns a pointer to an array that holds the absolute
pathname of the current working directory. The pointer is returned in the
ptr variable, which points to the
buf array where the pathname
is stored.
#include <stdlib.h>
#include <unistd.h>
...
long size;
char *buf;
char *ptr;
size = pathconf(".", _PC_PATH_MAX);
if ((buf = (char *)malloc((size_t)size)) != NULL)
ptr = getcwd(buf, (size_t)size);
...
None.
Since the maximum pathname length is arbitrary unless {PATH_MAX} is defined, an
application generally cannot supply a
buf with
size
{{PATH_MAX}+1}.
Having
getcwd() take no arguments and instead use the
malloc()
function to produce space for the returned argument was considered. The
advantage is that
getcwd() knows how big the working directory pathname
is and can allocate an appropriate amount of space. But the programmer would
have to use the
free() function to free the resulting object, or each
use of
getcwd() would further reduce the available memory. Also,
malloc() and
free() are used nowhere else in this volume of
IEEE Std 1003.1-2001. Finally,
getcwd() is taken from the
SVID where it has the two arguments used in this volume of
IEEE Std 1003.1-2001.
The older function
getwd() was rejected for use in this context because
it had only a buffer argument and no
size argument, and thus had no way
to prevent overwriting the buffer, except to depend on the programmer to
provide a large enough buffer.
On some implementations, if
buf is a null pointer,
getcwd() may
obtain
size bytes of memory using
malloc(). In this case, the
pointer returned by
getcwd() may be used as the argument in a
subsequent call to
free(). Invoking
getcwd() with
buf as
a null pointer is not recommended in conforming applications.
If a program is operating in a directory where some (grand)parent directory does
not permit reading,
getcwd() may fail, as in most implementations it
must read the directory to determine the name of the file. This can occur if
search, but not read, permission is granted in an intermediate directory, or
if the program is placed in that directory by some more privileged process
(for example, login). Including the [EACCES] error condition makes the
reporting of the error consistent and warns the application writer that
getcwd() can fail for reasons beyond the control of the application
writer or user. Some implementations can avoid this occurrence (for example,
by implementing
getcwd() using
pwd, where
pwd is a
set-user-root process), thus the error was made optional. Since this volume of
IEEE Std 1003.1-2001 permits the addition of other errors, this
would be a common addition and yet one that applications could not be expected
to deal with without this addition.
None.
malloc() , the Base Definitions volume of
IEEE Std 1003.1-2001,
<unistd.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html
.
