getcwd(3p) — Linux manual page


GETCWD(3P)              POSIX Programmer's Manual             GETCWD(3P)

PROLOG         top

       This manual page is part of the POSIX Programmer's Manual.  The
       Linux implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior),
       or the interface may not be implemented on Linux.

NAME         top

       getcwd — get the pathname of the current working directory

SYNOPSIS         top

       #include <unistd.h>

       char *getcwd(char *buf, size_t size);

DESCRIPTION         top

       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 shall contain no components that are
       dot or dot-dot, or are symbolic links.

       If there are multiple pathnames that getcwd() could place in the
       array pointed to by buf, one beginning with a single <slash>
       character and one or more beginning with two <slash> characters,
       then getcwd() shall place the pathname beginning with a single
       <slash> character in the array. The pathname shall not contain
       any unnecessary <slash> characters after the leading one or two
       <slash> characters.

       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.

RETURN VALUE         top

       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.

ERRORS         top

       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 string +1.

       The getcwd() function may fail if:

       EACCES Search permission was denied for the current directory, or
              read or search permission was denied for a directory above
              the current directory in the file hierarchy.

       ENOMEM Insufficient storage space is available.

       The following sections are informative.

EXAMPLES         top

       The following example uses {PATH_MAX} as the initial buffer size
       (unless it is indeterminate or very large), and calls getcwd()
       with progressively larger buffers until it does not give an
       [ERANGE] error.

           #include <stdlib.h>
           #include <errno.h>
           #include <unistd.h>


           long path_max;
           size_t size;
           char *buf;
           char *ptr;

           path_max = pathconf(".", _PC_PATH_MAX);
           if (path_max == -1)
               size = 1024;
           else if (path_max > 10240)
               size = 10240;
               size = path_max;

           for (buf = ptr = NULL; ptr == NULL; size *= 2)
               if ((buf = realloc(buf, size)) == NULL)
                   ... handle error ...

               ptr = getcwd(buf, size);
               if (ptr == NULL && errno != ERANGE)
                   ... handle error ...
           free (buf);


       If the pathname obtained from getcwd() is longer than {PATH_MAX}
       bytes, it could produce an [ENAMETOOLONG] error if passed to
       chdir().  Therefore, in order to return to that directory it may
       be necessary to break the pathname into sections shorter than
       {PATH_MAX} bytes and call chdir() on each section in turn (the
       first section being an absolute pathname and subsequent sections
       being relative pathnames). A simpler way to handle saving and
       restoring the working directory when it may be deeper than
       {PATH_MAX} bytes in the file hierarchy is to use a file
       descriptor and fchdir(), rather than getcwd() and chdir().
       However, the two methods do have some differences. The fchdir()
       approach causes the program to restore a working directory even
       if it has been renamed in the meantime, whereas the chdir()
       approach restores to a directory with the same name as the
       original, even if the directories were renamed in the meantime.
       Since the fchdir() approach does not access parent directories,
       it can succeed when getcwd() would fail due to permissions
       problems. In applications conforming to earlier versions of this
       standard, it was not possible to use the fchdir() approach when
       the working directory is searchable but not readable, as the only
       way to open a directory was with O_RDONLY, whereas the getcwd()
       approach can succeed in this case.

RATIONALE         top

       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. Finally, getcwd() is
       taken from the SVID where it has the two arguments used in this
       volume of POSIX.1‐2017.

       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.

       Earlier implementations of getcwd() sometimes generated pathnames
       like "../../../subdirname" internally, using them to explore the
       path of ancestor directories back to the root. If one of these
       internal pathnames exceeded {PATH_MAX} in length, the
       implementation could fail with errno set to [ENAMETOOLONG].  This
       is no longer allowed.

       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
       developer that getcwd() can fail for reasons beyond the control
       of the application developer 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 POSIX.1‐2017 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.



SEE ALSO         top


       The Base Definitions volume of POSIX.1‐2017, unistd.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 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 .

       Any typographical or formatting errors that appear in this page
       are most likely to have been introduced during the conversion of
       the source files to man page format. To report such errors, see .

IEEE/The Open Group               2017                        GETCWD(3P)

Pages that refer to this page: unistd.h(0p)pwd(1p)chdir(3p)realpath(3p)