B.2.3 The Configuration Process

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 1990 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 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.