man3/getcwd.3

   1 .\" (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
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  23 .\" Modified Wed Jul 21 22:35:42 1993 by Rik Faith (faith@cs.unc.edu)
  24 .\" Modified 18 Mar 1996 by Martin Schulze (joey@infodrom.north.de):
  25 .\"   Corrected description of getwd().
  26 .\" Modified Sat Aug 21 12:32:12 MET 1999 by aeb - applied fix by aj
  27 .\" Modified Mon Dec 11 13:32:51 MET 2000 by aeb
  28 .\" Modified Thu Apr 22 03:49:15 CEST 2002 by Roger Luethi <rl@hellgate.ch>
  29 .\"
  30 .TH GETCWD 3 2002-04-22 "GNU" "Linux Programmer's Manual"
  31 .SH NAME
  32 getcwd, get_current_dir_name, getwd \- Get current working directory
  33 .SH SYNOPSIS
  34 .nf
  35 .B #include <unistd.h>
  36 .sp
  37 .BI "char *getcwd(char *" buf ", size_t " size );
  38 .B "char *get_current_dir_name(void);"
  39 .BI "char *getwd(char *" buf );
  40 .fi
  41 .SH DESCRIPTION
  42 The
  43 .BR getcwd ()
  44 function copies an absolute pathname of the current working directory
  45 to the array pointed to by
  46 .IR buf ,
  47 which is of length
  48 .IR size .
  49 .PP
  50 If the current absolute path name would require a buffer longer than
  51 .I size
  52 elements, NULL is returned, and
  53 .I errno
  54 is set to
  55 .BR ERANGE ;
  56 an application should check for this error, and allocate a larger
  57 buffer if necessary.
  58 .PP
  59 If
  60 .I buf
  61 is NULL, the behaviour of
  62 .BR getcwd ()
  63 is undefined.
  64 .PP
  65 As an extension to the POSIX.1 standard, Linux (libc4, libc5, glibc)
  66 .BR getcwd ()
  67 allocates the buffer dynamically using
  68 .BR malloc ()
  69 if
  70 .I buf
  71 is NULL on call.
  72 In this case, the allocated buffer has the length
  73 .I size
  74 unless
  75 .I size
  76 is zero, when
  77 .I buf
  78 is allocated as big as necessary.  It is possible (and, indeed,
  79 advisable) to
  80 .BR free ()
  81 the buffers if they have been obtained this way.
  82
  83 .BR get_current_dir_name (),
  84 which is only prototyped if
  85 .B _GNU_SOURCE
  86 is defined, will
  87 .BR malloc (3)
  88 an array big enough to hold the current directory name.  If the environment
  89 variable
  90 .B PWD
  91 is set, and its value is correct, then that value will be returned.
  92
  93 .BR getwd (),
  94 which is only prototyped if
  95 .B _BSD_SOURCE
  96 or
  97 .B _XOPEN_SOURCE_EXTENDED
  98 is defined, will not
  99 .BR malloc (3)
 100 any memory. The
 101 .I buf
 102 argument should be a pointer to an array at least
 103 .B PATH_MAX
 104 bytes long.
 105 .BR getwd ()
 106 does only return the first
 107 .B PATH_MAX
 108 bytes of the actual pathname.
 109 Note that
 110 .B PATH_MAX
 111 need not be a compile-time constant; it may depend on the filesystem
 112 and may even be unlimited. For portability and security reasons, use of
 113 .BR getwd ()
 114 is deprecated.
 115 .SH "RETURN VALUE"
 116 NULL
 117 on failure with
 118 .I errno
 119 set accordingly, and
 120 .I buf
 121 on success. The contents of the array pointed to by
 122 .IR buf
 123 is undefined on error.
 124 .SH ERRORS
 125 .TP
 126 .B EACCES
 127 Permission to read or search a component of the filename was denied.
 128 .TP
 129 .B EFAULT
 130 .IR buf
 131 points to a bad address.
 132 .TP
 133 .B EINVAL
 134 The
 135 .IR size
 136 argument is zero and
 137 .IR buf
 138 is not a null pointer.
 139 .TP
 140 .B ENOENT
 141 The current working directory has been unlinked.
 142 .TP
 143 .B ERANGE
 144 The
 145 .IR size
 146 argument is less than the length of the working directory name.
 147 You need to allocate a bigger array and try again.
 148 .SH NOTES
 149 Under Linux, the function
 150 .BR getcwd ()
 151 is a system call (since 2.1.92).
 152 On older systems it would query
 153 .IR /proc/self/cwd .
 154 If both system call and proc file system are missing, a
 155 generic implementation is called. Only in that case can
 156 these calls fail under Linux with
 157 .BR EACCES .
 158 .LP
 159 These functions are often used to save the location of the current working
 160 directory for the purpose of returning to it later. Opening the current
 161 directory (".") and calling
 162 .BR fchdir (2)
 163 to return is usually a faster and more reliable alternative when sufficiently
 164 many file descriptors are available, especially on platforms other than Linux.
 165 .SH "CONFORMING TO"
 166 POSIX.1
 167 .SH "SEE ALSO"
 168 .BR chdir (2),
 169 .BR fchdir (2),
 170 .BR open (2),
 171 .BR unlink (2),
 172 .BR free (3),
 173 .BR malloc (3)