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getcwd(3) [netbsd man page]

GETCWD(3)						   BSD Library Functions Manual 						 GETCWD(3)

NAME
getcwd, getwd -- get working directory pathname LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <unistd.h> char * getcwd(char *buf, size_t size); char * getwd(char *buf); DESCRIPTION
The getcwd() function copies the absolute pathname of the current working directory into the memory referenced by buf and returns a pointer to buf. The size argument is the size, in bytes, of the array referenced by buf. If buf is NULL, space is allocated as necessary to store the pathname. This space may later be free(3)'d. The function getwd() is a compatibility routine which calls getcwd() with its buf argument and a size of MAXPATHLEN (as defined in the include file <sys/param.h>). Obviously, buf should be at least MAXPATHLEN bytes in length. These routines have traditionally been used by programs to save the name of a working directory for the purpose of returning to it. A much faster and less error-prone method of accomplishing this is to open the current directory ('.') and use the fchdir(2) function to return. RETURN VALUES
Upon successful completion, a pointer to the pathname is returned. Otherwise a NULL pointer is returned and the global variable errno is set to indicate the error. In addition, getwd() copies the error message associated with errno into the memory referenced by buf. ERRORS
The getcwd() function will fail if: [EACCES] Read or search permission was denied for a component of the pathname. [EINVAL] The size argument is zero. [ENOENT] A component of the pathname no longer exists. [ENOMEM] Insufficient memory is available. [ERANGE] The size argument is greater than zero but smaller than the length of the pathname plus 1. SEE ALSO
chdir(2), fchdir(2), malloc(3), strerror(3) STANDARDS
The getwd() and getcwd() functions conform to ISO/IEC 9945-1:1990 (``POSIX.1''). The IEEE Std 1003.1-2004 (``POSIX.1'') revision marked getwd() as legacy and recommended the use of getcwd() instead. The IEEE Std 1003.1-2008 (``POSIX.1'') revision removed getwd() from the specification. The ability to specify a NULL pointer and have getcwd() allocate memory as necessary is an extension. HISTORY
The getwd() function appeared in 4.0BSD. SECURITY CONSIDERATIONS
As getwd() does not know the length of the supplied buffer, it is possible for a long (but valid) path to overflow the buffer and provide a means for an attacker to exploit the caller. getcwd() should be used in place of getwd() (the latter is only provided for compatibility pur- poses). BSD
April 29, 2010 BSD

Check Out this Related Man Page

GETCWD(3)						     Linux Programmer's Manual							 GETCWD(3)

NAME
getcwd, get_current_dir_name, getwd - Get current working directory SYNOPSIS
#include <unistd.h> char *getcwd(char *buf, size_t size); char *get_current_dir_name(void); char *getwd(char *buf); DESCRIPTION
The getcwd() function copies an 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 appli- cation should check for this error, and allocate a larger buffer if necessary. 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 rea- sons, use of getwd is deprecated. RETURN VALUE
NULL on failure with errno set accordingly, and buf on success. The contents of the array pointed to by buf is undefined on error. ERRORS
EACCES Permission to read or search a component of the file name was denied. EFAULT buf points to a bad address. EINVAL The size argument is zero and buf is not a null pointer. ENOENT The current working directory has been unlinked. ERANGE The size argument is less than the length of the working directory name. You need to allocate a bigger array and try again. NOTES
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. CONFORMING TO
POSIX.1 SEE ALSO
chdir(2), fchdir(2), open(2), unlink(2), free(3), malloc(3) GNU
2002-04-22 GETCWD(3)
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