Originální popis anglicky:
confstr - get configurable variables
Návod, kniha: POSIX Programmer's Manual
#include <unistd.h>
size_t confstr(int
name, char
*buf , size_t
len);
The
confstr() function shall return configuration-defined string values.
Its use and purpose are similar to
sysconf(), but it is used where
string values rather than numeric values are returned.
The
name argument represents the system variable to be queried. The
implementation shall support the following name values, defined in
<unistd.h>. It may support others:
_CS_PATH
_CS_POSIX_V6_ILP32_OFF32_CFLAGS
_CS_POSIX_V6_ILP32_OFF32_LDFLAGS
_CS_POSIX_V6_ILP32_OFF32_LIBS
_CS_POSIX_V6_ILP32_OFFBIG_CFLAGS
_CS_POSIX_V6_ILP32_OFFBIG_LDFLAGS
_CS_POSIX_V6_ILP32_OFFBIG_LIBS
_CS_POSIX_V6_LP64_OFF64_CFLAGS
_CS_POSIX_V6_LP64_OFF64_LDFLAGS
_CS_POSIX_V6_LP64_OFF64_LIBS
_CS_POSIX_V6_LPBIG_OFFBIG_CFLAGS
_CS_POSIX_V6_LPBIG_OFFBIG_LDFLAGS
_CS_POSIX_V6_LPBIG_OFFBIG_LIBS
_CS_POSIX_V6_WIDTH_RESTRICTED_ENVS
_CS_XBS5_ILP32_OFF32_CFLAGS (
LEGACY)
_CS_XBS5_ILP32_OFF32_LDFLAGS (
LEGACY)
_CS_XBS5_ILP32_OFF32_LIBS (
LEGACY)
_CS_XBS5_ILP32_OFF32_LINTFLAGS (
LEGACY)
_CS_XBS5_ILP32_OFFBIG_CFLAGS (
LEGACY)
_CS_XBS5_ILP32_OFFBIG_LDFLAGS (
LEGACY)
_CS_XBS5_ILP32_OFFBIG_LIBS (
LEGACY)
_CS_XBS5_ILP32_OFFBIG_LINTFLAGS (
LEGACY)
_CS_XBS5_LP64_OFF64_CFLAGS (
LEGACY)
_CS_XBS5_LP64_OFF64_LDFLAGS (
LEGACY)
_CS_XBS5_LP64_OFF64_LIBS (
LEGACY)
_CS_XBS5_LP64_OFF64_LINTFLAGS (
LEGACY)
_CS_XBS5_LPBIG_OFFBIG_CFLAGS (
LEGACY)
_CS_XBS5_LPBIG_OFFBIG_LDFLAGS (
LEGACY)
_CS_XBS5_LPBIG_OFFBIG_LIBS (
LEGACY)
_CS_XBS5_LPBIG_OFFBIG_LINTFLAGS (
LEGACY)
If
len is not 0, and if
name has a configuration-defined value,
confstr() shall copy that value into the
len-byte buffer pointed
to by
buf. If the string to be returned is longer than
len
bytes, including the terminating null, then
confstr() shall truncate
the string to
len-1 bytes and null-terminate the result. The
application can detect that the string was truncated by comparing the value
returned by
confstr() with
len.
If
len is 0 and
buf is a null pointer, then
confstr() shall
still return the integer value as defined below, but shall not return a
string. If
len is 0 but
buf is not a null pointer, the result is
unspecified.
If the implementation supports the POSIX shell option, the string stored in
buf after a call to:
confstr(_CS_PATH, buf, sizeof(buf))
can be used as a value of the
PATH environment variable that accesses all
of the standard utilities of IEEE Std 1003.1-2001, if the return
value is less than or equal to
sizeof(
buf).
If
name has a configuration-defined value,
confstr() shall return
the size of buffer that would be needed to hold the entire
configuration-defined value including the terminating null. If this return
value is greater than
len, the string returned in
buf is
truncated.
If
name is invalid,
confstr() shall return 0 and set
errno
to indicate the error.
If
name does not have a configuration-defined value,
confstr()
shall return 0 and leave
errno unchanged.
The
confstr() function shall fail if:
- EINVAL
- The value of the name argument is invalid.
The following sections are informative.
None.
An application can distinguish between an invalid
name parameter value
and one that corresponds to a configurable variable that has no
configuration-defined value by checking if
errno is modified. This
mirrors the behavior of
sysconf().
The original need for this function was to provide a way of finding the
configuration-defined default value for the environment variable
PATH .
Since
PATH can be modified by the user to include directories that
could contain utilities replacing the standard utilities in the Shell and
Utilities volume of IEEE Std 1003.1-2001, applications need a
way to determine the system-supplied
PATH environment variable value
that contains the correct search path for the standard utilities.
An application could use:
confstr(name, (char *)NULL, (size_t)0)
to find out how big a buffer is needed for the string value; use
malloc()
to allocate a buffer to hold the string; and call
confstr() again to
get the string. Alternately, it could allocate a fixed, static buffer that is
big enough to hold most answers (perhaps 512 or 1024 bytes), but then use
malloc() to allocate a larger buffer if it finds that this is too
small.
Application developers can normally determine any configuration variable by
means of reading from the stream opened by a call to:
popen("command -p getconf variable", "r");
The
confstr() function with a
name argument of _CS_PATH returns a
string that can be used as a
PATH environment variable setting that
will reference the standard shell and utilities as described in the Shell and
Utilities volume of IEEE Std 1003.1-2001.
The
confstr() function copies the returned string into a buffer supplied
by the application instead of returning a pointer to a string. This allows a
cleaner function in some implementations (such as those with lightweight
threads) and resolves questions about when the application must copy the
string returned.
None.
pathconf() ,
sysconf() , the Base Definitions volume of
IEEE Std 1003.1-2001,
<unistd.h>, the Shell and
Utilities volume of IEEE Std 1003.1-2001,
c99
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. 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.opengroup.org/unix/online.html
.
