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pathconf
Gets configuration variable for path name.
Syntax
#include <unistd.h>
long pathconf(char *pathname, int name);
Parameters
pathname is the name of the file or directory.
name is a symbol indicating the variable, the value of which
you want to determine, relative to the file or directory
specified in pathname. .
Description
pathconf() lets you determine the value of a configuration variable
associated with a particular file. If pathconf() can determine the value
of the requested variable, it returns that value as its result.
The name argument may be any one of a set of symbols defined in
<unistd.h>. Each symbol stands for a configuration variable. The
following list shows the possible symbols and the variables that each
symbol stands for:
_PC_LINK_MAX stands for LINK_MAX defined in <limits.h>--the
maximum number of links the file can have. If
pathname is a directory, pathconf() returns the
maximum number of links which can be established
to the directory itself.
_PC_MAX_CANON stands for MAX_CANON defined in <limits.h>--the
maximum number of bytes in a terminal canonical
input line. pathname must refer to a terminal
file.
_PC_MAX_INPUT stands for MAX_INPUT defined in <limits.h>--the
minimum number of bytes for which space is
available in a terminal input queue, which means
the maximum number of bytes that a portable
application may have the user enter before the
application actually reads the input. pathname
must refer to a terminal file.
_PC_NAME_MAX stands for NAME_MAX defined in <limits.h>--the
maximum number of characters in a filename (not
including any terminating 0 if the filename is
stored as a string). This only refers to the
filename itself, that is, the last component of
the file's path name. pathname must be a
directory, and pathconf() returns the maximum
length of filenames for files in the directory.
_PC_PATH_MAX stands for PATH_MAX defined in <limits.h>--the
maximum number of characters in a complete path
name (not including any terminating \0 if the path
name is stored as a string). pathname must be a
directory, and pathconf() returns the maximum
length of a relative path name when the specified
directory is the working directory.
_PC_PIPE_BUF stands for PIPE_BUF defined in <limits.h>--the
maximum number of bytes that can be written
`atomically' to a pipe. If more than this number
of bytes are written to a pipe, the operation may
take more than one physical write operation and
may require more than one physical read operation
to read the data on the other end of the pipe. If
pathname is a FIFO file, pathconf() returns the
value for the file itself. If pathname is a
directory, pathconf() returns the value for any
FIFOs which exist or can be created under the
directory. If pathname is any other kind of file,
the behavior is undefined.
_PC_CHOWN _RESTRICTED stands for _POSIX_CHOWN_RESTRICTED defined in the
<unistd.h>. This indicates that the use of the
chown() function is restricted--see chown() for
more details. If pathname is a directory,
pathconf() returns the value for any kind of file
under the directory, but not for subdirectories of
the directory.
_PC_NO_TRUNC stands for _POSIX_NO_TRUNC defined in <unistd.h>.
This indicates that an error is to be generated if
a file name is longer than NAME_MAX. pathname must
be a directory, and the value returned by
pathconf() applies to all files under that
directory.
_PC_VDISABLE stands for _POSIX_VDISABLE defined in <unistd.h>.
This indicates that terminal special characters
can be disabled using this character value, if it
is defined; see tcsetattr() for details. pathname
must refer to a terminal file.
For _POSIX_CHOWN_RESTRICTED, _POSIX_NO_TRUNC, and _POSIX_VDISABLE,
pathconf() returns -1 if the option is turned off and another value
otherwise.
If a particular variable has no limit (for example PATH_MAX), pathconf()
returns -1 but does not change errno.
Errors
If pathconf() cannot determine an appropriate value, it returns -1 and
sets errno to one of the following:
EACCES CAUSE The process does not have search permission on some
component of the pathname prefix.
ACTION Ensure that the process has search permissions on all
components of the pathname prefix.
EINVAL CAUSE name is not a valid variable code, or the given
variable cannot be associated with the specified
file.
ACTION Ensure that name is a valid variable code.
Table 4-0. (cont.)
ENAMETOOLONG CAUSE pathname is longer than PATH_MAX characters, or some
component of pathname is longer than NAME_MAX and
_POSIX_NO_TRUNC is set.
ACTION Unset the configuration variable _POSIX_NO_TRUNC' to
disable checking the length of pathname or modify
pathname to ensure that the entire name is less than
PATH_MAX characters in length and that each component
is less than NAME_MAX characters in length.
ENOENT CAUSE There is no filenamed pathname, or the pathname
argument is an empty string.
ACTION Ensure that you provide a pathname and that pathname
is a valid file.
ENOTDIR CAUSE Some component of the pathname prefix is not a
directory.
ACTION Ensure that all components of pathname are valid
directories.
See Also
fpathconf()