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