This section 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
(see Reporting Problems and 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.