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 2007-07-26 "GNU" "Linux Programmer's Manual"
  31 .SH NAME
  32 getcwd, getwd, get_current_dir_name \- 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 .sp
  39 .BI "char *getwd(char *" buf );
  40 .sp
  41 .B "char *get_current_dir_name(void);"
  42 .fi
  43 .sp
  44 .in -4n
  45 Feature Test Macro Requirements for glibc (see
  46 .BR feature_test_macros (7)):
  47 .in
  48 .sp
  49 .BR getcwd ():
  50 _BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500
  51 .br
  52 .BR get_current_dir_name ():
  53 _GNU_SOURCE
  54 .SH DESCRIPTION
  55 The
  56 .BR getcwd ()
  57 function copies an absolute pathname of the current working directory
  58 to the array pointed to by
  59 .IR buf ,
  60 which is of length
  61 .IR size .
  62 .PP
  63 If the current absolute pathname would require a buffer longer than
  64 .I size
  65 elements, NULL is returned, and
  66 .I errno
  67 is set to
  68 .BR ERANGE ;
  69 an application should check for this error, and allocate a larger
  70 buffer if necessary.
  71 .PP
  72 If
  73 .I buf
  74 is NULL, the behavior of
  75 .BR getcwd ()
  76 is undefined.
  77 .PP
  78 As an extension to the POSIX.1-2001 standard, Linux (libc4, libc5, glibc)
  79 .BR getcwd ()
  80 allocates the buffer dynamically using
  81 .BR malloc (3)
  82 if
  83 .I buf
  84 is NULL on call.
  85 In this case, the allocated buffer has the length
  86 .I size
  87 unless
  88 .I size
  89 is zero, when
  90 .I buf
  91 is allocated as big as necessary.
  92 It is possible (and, indeed,
  93 advisable) to
  94 .BR free (3)
  95 the buffers if they have been obtained this way.
  96
  97 .BR get_current_dir_name (),
  98 will
  99 .BR malloc (3)
 100 an array big enough to hold the current directory name.
 101 If the environment
 102 variable
 103 .B PWD
 104 is set, and its value is correct, then that value will be returned.
 105
 106 .BR getwd (),
 107 does not
 108 .BR malloc (3)
 109 any memory.
 110 The
 111 .I buf
 112 argument should be a pointer to an array at least
 113 .B PATH_MAX
 114 bytes long.
 115 .BR getwd ()
 116 does only return the first
 117 .B PATH_MAX
 118 bytes of the actual pathname.
 119 Note that
 120 .B PATH_MAX
 121 need not be a compile-time constant; it may depend on the file system
 122 and may even be unlimited.
 123 For portability and security reasons, use of
 124 .BR getwd ()
 125 is deprecated.
 126 .SH "RETURN VALUE"
 127 NULL
 128 on failure with
 129 .I errno
 130 set accordingly, and
 131 .I buf
 132 on success.
 133 The contents of the array pointed to by
 134 .I buf
 135 is undefined on error.
 136 .SH ERRORS
 137 .TP
 138 .B EACCES
 139 Permission to read or search a component of the filename was denied.
 140 .TP
 141 .B EFAULT
 142 .I buf
 143 points to a bad address.
 144 .TP
 145 .B EINVAL
 146 The
 147 .I size
 148 argument is zero and
 149 .I buf
 150 is not a null pointer.
 151 .TP
 152 .B ENOENT
 153 The current working directory has been unlinked.
 154 .TP
 155 .B ERANGE
 156 The
 157 .I size
 158 argument is less than the length of the working directory name.
 159 You need to allocate a bigger array and try again.
 160 .SH "CONFORMING TO"
 161 .BR getcwd ()
 162 conforms to POSIX.1-2001.
 163 .BR getwd ()
 164 is present in POSIX.1-2001, but marked LEGACY.
 165 .BR get_current_dir_name ()
 166 is a GNU extension.
 167 .SH NOTES
 168 Under Linux, the function
 169 .BR getcwd ()
 170 is a system call (since 2.1.92).
 171 On older systems it would query
 172 .IR /proc/self/cwd .
 173 If both system call and proc file system are missing, a
 174 generic implementation is called.
 175 Only in that case can
 176 these calls fail under Linux with
 177 .BR EACCES .
 178 .LP
 179 These functions are often used to save the location of the current working
 180 directory for the purpose of returning to it later.
 181 Opening the current
 182 directory (".") and calling
 183 .BR fchdir (2)
 184 to return is usually a faster and more reliable alternative when sufficiently
 185 many file descriptors are available, especially on platforms other than Linux.
 186 .SH "SEE ALSO"
 187 .BR chdir (2),
 188 .BR fchdir (2),
 189 .BR open (2),
 190 .BR unlink (2),
 191 .BR free (3),
 192 .BR malloc (3)