diff options
Diffstat (limited to 'man-pages-posix-2013/man3p/getcwd.3p')
| -rw-r--r-- | man-pages-posix-2013/man3p/getcwd.3p | 292 |
1 files changed, 292 insertions, 0 deletions
diff --git a/man-pages-posix-2013/man3p/getcwd.3p b/man-pages-posix-2013/man3p/getcwd.3p new file mode 100644 index 0000000..2cf9a50 --- /dev/null +++ b/man-pages-posix-2013/man3p/getcwd.3p @@ -0,0 +1,292 @@ +'\" et +.TH GETCWD "3P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual" +.SH PROLOG +This manual page is part of the POSIX Programmer's Manual. +The Linux implementation of this interface may differ (consult +the corresponding Linux manual page for details of Linux behavior), +or the interface may not be implemented on Linux. + +.SH NAME +getcwd +\(em get the pathname of the current working directory +.SH SYNOPSIS +.LP +.nf +#include <unistd.h> +.P +char *getcwd(char *\fIbuf\fP, size_t \fIsize\fP); +.fi +.SH DESCRIPTION +The +\fIgetcwd\fR() +function shall place an absolute pathname of the current working directory +in the array pointed to by +.IR buf , +and return +.IR buf . +The pathname shall contain no components that are dot or dot-dot, or +are symbolic links. +.P +If there are multiple pathnames that +\fIgetcwd\fR() +could place in the array pointed to by +.IR buf , +one beginning with a single +<slash> +character and one or more beginning with two +<slash> +characters, then +\fIgetcwd\fR() +shall place the pathname beginning with a single +<slash> +character in the array. The pathname shall not contain any unnecessary +<slash> +characters after the leading one or two +<slash> +characters. +.P +The +.IR size +argument is the size in bytes of the character array pointed to by the +.IR buf +argument. If +.IR buf +is a null pointer, the behavior of +\fIgetcwd\fR() +is unspecified. +.SH "RETURN VALUE" +Upon successful completion, +\fIgetcwd\fR() +shall return the +.IR buf +argument. Otherwise, +\fIgetcwd\fR() +shall return a null pointer and set +.IR errno +to indicate the error. The contents of the array pointed to by +.IR buf +are then undefined. +.SH ERRORS +The +\fIgetcwd\fR() +function shall fail if: +.TP +.BR EINVAL +The +.IR size +argument is 0. +.TP +.BR ERANGE +The +.IR size +argument is greater than 0, but is smaller than the length of +the string +1. +.P +The +\fIgetcwd\fR() +function may fail if: +.TP +.BR EACCES +Search permission was denied for the current directory, or read or search +permission was denied for a directory above the current directory in +the file hierarchy. +.TP +.BR ENOMEM +Insufficient storage space is available. +.LP +.IR "The following sections are informative." +.SH EXAMPLES +The following example uses +{PATH_MAX} +as the initial buffer size (unless it is indeterminate or very large), +and calls +\fIgetcwd\fR() +with progressively larger buffers until it does not give an +.BR [ERANGE] +error. +.sp +.RS 4 +.nf +\fB +#include <stdlib.h> +#include <errno.h> +#include <unistd.h> +.P +\&... +.P +long path_max; +size_t size; +char *buf; +char *ptr; +.P +path_max = pathconf(".", _PC_PATH_MAX); +if (path_max == -1) + size = 1024; +else if (path_max > 10240) + size = 10240; +else + size = path_max; +.P +for (buf = ptr = NULL; ptr == NULL; size *= 2) +{ + if ((buf = realloc(buf, size)) == NULL) + { + ... handle error ... + } +.P + ptr = getcwd(buf, size); + if (ptr == NULL && errno != ERANGE) + { + ... handle error ... + } +} +\&... +free (buf); +.fi \fR +.P +.RE +.SH "APPLICATION USAGE" +If the pathname obtained from +\fIgetcwd\fR() +is longer than +{PATH_MAX} +bytes, it could produce an +.BR [ENAMETOOLONG] +error if passed to +\fIchdir\fR(). +Therefore, in order to return to that directory it may be necessary to +break the pathname into sections shorter than +{PATH_MAX} +bytes and call +\fIchdir\fR() +on each section in turn (the first section being an absolute pathname and +subsequent sections being relative pathnames). A simpler way to handle +saving and restoring the working directory when it may be deeper than +{PATH_MAX} +bytes in the file hierarchy is to use a file descriptor and +\fIfchdir\fR(), +rather than +\fIgetcwd\fR() +and +\fIchdir\fR(). +However, the two methods do have some differences. The +\fIfchdir\fR() +approach causes the program to restore a working directory even +if it has been renamed in the meantime, whereas the +\fIchdir\fR() +approach restores to a directory with the same name as the original, +even if the directories were renamed in the meantime. Since the +\fIfchdir\fR() +approach does not access parent directories, it can succeed when +\fIgetcwd\fR() +would fail due to permissions problems. In applications conforming to +earlier versions of this standard, it was not possible to use the +\fIfchdir\fR() +approach when the working directory is searchable but not readable, +as the only way to open a directory was with O_RDONLY, whereas the +\fIgetcwd\fR() +approach can succeed in this case. +.SH RATIONALE +Having +\fIgetcwd\fR() +take no arguments and instead use the +\fImalloc\fR() +function to produce space for the returned argument was considered. +The advantage is that +\fIgetcwd\fR() +knows how big the working directory pathname is and can allocate an +appropriate amount of space. But the programmer would have to use the +\fIfree\fR() +function to free the resulting object, or each use of +\fIgetcwd\fR() +would further reduce the available memory. Finally, +\fIgetcwd\fR() +is taken from the SVID where it has the two arguments used in this volume of POSIX.1\(hy2008. +.P +The older function +.IR getwd (\|) +was rejected for use in this context because it had only a buffer +argument and no +.IR size +argument, and thus had no way to prevent overwriting the buffer, except +to depend on the programmer to provide a large enough buffer. +.P +On some implementations, if +.IR buf +is a null pointer, +\fIgetcwd\fR() +may obtain +.IR size +bytes of memory using +\fImalloc\fR(). +In this case, the pointer returned by +\fIgetcwd\fR() +may be used as the argument in a subsequent call to +\fIfree\fR(). +Invoking +\fIgetcwd\fR() +with +.IR buf +as a null pointer is not recommended in conforming applications. +.P +Earlier implementations of +\fIgetcwd\fR() +sometimes generated pathnames like +.BR \(dq../../../subdirname\(dq +internally, using them to explore the path of ancestor directories back +to the root. If one of these internal pathnames exceeded +{PATH_MAX} +in length, the implementation could fail with +.IR errno +set to +.BR [ENAMETOOLONG] . +This is no longer allowed. +.P +If a program is operating in a directory where some (grand)parent +directory does not permit reading, +\fIgetcwd\fR() +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 +.BR [EACCES] +error condition makes the reporting of the error consistent and warns +the application developer that +\fIgetcwd\fR() +can fail for reasons beyond the control of the application developer or +user. Some implementations can avoid this occurrence (for example, by +implementing +\fIgetcwd\fR() +using +.IR pwd , +where +.IR pwd +is a set-user-root process), +thus the error was made optional. Since this volume of POSIX.1\(hy2008 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. +.SH "FUTURE DIRECTIONS" +None. +.SH "SEE ALSO" +.IR "\fImalloc\fR\^(\|)" +.P +The Base Definitions volume of POSIX.1\(hy2008, +.IR "\fB<unistd.h>\fP" +.SH COPYRIGHT +Portions of this text are reprinted and reproduced in electronic form +from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology +-- Portable Operating System Interface (POSIX), The Open Group Base +Specifications Issue 7, Copyright (C) 2013 by the Institute of +Electrical and Electronics Engineers, Inc and The Open Group. +(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html . + +Any typographical or formatting errors that appear +in this page are most likely +to have been introduced during the conversion of the source files to +man page format. To report such errors, see +https://www.kernel.org/doc/man-pages/reporting_bugs.html . |