File: gawk.info,  Node: Configuration Philosophy,  Next: Compiling from Git,  Prev: Additional Configuration Options,  Up: Unix Installation

B.2.4 The Configuration Process
-------------------------------

This minor node is of interest only if you know something about using
the C language and Unix-like operating systems.

   The source code for 'gawk' generally attempts to adhere to formal
standards wherever possible.  This means that 'gawk' uses library
routines that are specified by the ISO C standard and by the POSIX
operating system interface standard.  The 'gawk' source code requires
using an ISO C compiler (the 1999 standard).

   Many Unix systems do not support all of either the ISO or the POSIX
standards.  The 'missing_d' subdirectory in the 'gawk' distribution
contains replacement versions of those functions that are most likely to
be missing.

   The 'config.h' file that 'configure' creates contains definitions
that describe features of the particular operating system where you are
attempting to compile 'gawk'.  The three things described by this file
are: what header files are available, so that they can be correctly
included, what (supposedly) standard functions are actually available in
your C libraries, and various miscellaneous facts about your operating
system.  For example, there may not be an 'st_blksize' element in the
'stat' structure.  In this case, 'HAVE_STRUCT_STAT_ST_BLKSIZE' is
undefined.

   It is possible for your C compiler to lie to 'configure'.  It may do
so by not exiting with an error when a library function is not
available.  To get around this, edit the 'custom.h' file.  Use an
'#ifdef' that is appropriate for your system, and either '#define' any
constants that 'configure' should have defined but didn't, or '#undef'
any constants that 'configure' defined and should not have.  The
'custom.h' file is automatically included by the 'config.h' file.

   It is also possible that the 'configure' program generated by
Autoconf will not work on your system in some other fashion.  If you do
have a problem, the 'configure.ac' file is the input for Autoconf.  You
may be able to change this file and generate a new version of
'configure' that works on your system (*note Bugs:: for information on
how to report problems in configuring 'gawk').  The same mechanism may
be used to send in updates to 'configure.ac' and/or 'custom.h'.