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CONFSTR(P) CONFSTR(P)
NAME
confstr - get configurable variables
SYNOPSIS
#include <unistd.h>
size_t confstr(int name, char *buf, size_t len);
DESCRIPTION
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 oth-
ers:
_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 appli-
cation 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 inte-
ger 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).
RETURN VALUE
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 includ-
ing 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.
ERRORS
The confstr() function shall fail if:
EINVAL The value of the name argument is invalid.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
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 configura-
tion-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 allo-
cate 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.
RATIONALE
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 func-
tion in some implementations (such as those with lightweight threads) and resolves
questions about when the application must copy the string returned.
FUTURE DIRECTIONS
None.
SEE ALSO
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
COPYRIGHT
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 .
POSIX 2003 CONFSTR(P)
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