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GETCWD

GETCWD

Section: POSIX Programmer's Manual (P) Updated: 2003
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NAME

getcwd - get the pathname of the current working directory  

SYNOPSIS

#include <unistd.h>

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

DESCRIPTION

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.  

RETURN VALUE

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

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.  

EXAMPLES

 

Determining the Absolute Pathname of the Current Working Directory

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);
...

 

APPLICATION USAGE

None.  

RATIONALE

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.  

FUTURE DIRECTIONS

None.  

SEE ALSO

malloc() , the Base Definitions volume of IEEE Std 1003.1-2001, <unistd.h>  

COPYRIGHT

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 .


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
EXAMPLES
Determining the Absolute Pathname of the Current Working Directory
APPLICATION USAGE
RATIONALE
FUTURE DIRECTIONS
SEE ALSO
COPYRIGHT

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Time: 21:46:40 GMT, April 16, 2011