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CONFSTR(3P)                POSIX Programmer's Manual               CONFSTR(3P)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may dif-
       fer (consult the corresponding Linux manual page for details of Linux behavior), or the interface  may  not  be
       implemented on Linux.

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 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).

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 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.

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  config-
       urable  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 con-
       tain 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 cor-
       rect 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.

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  return-
       ing  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.

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, Stan-
       dard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base  Specifica-
       tions  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 Stan-
       dard,  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 .



IEEE/The Open Group                  2003                          CONFSTR(3P)