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
       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.

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 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,
       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 .

IEEE/The Open Group                                   2003                                            CONFSTR(P)