C.2 autoheader

autoheader runs m4 over `configure.in', but with key macros defined differently than when autoconf is executed, such that suitable cpp definitions are output to `config.h.in'.

user input files optional input process output files ================ ============== ======= ============ aclocal.m4 - - - - - - - . (acconfig.h) - - - -. | V V .----------, configure.in ----------------------->|autoheader|----> config.h.in `----------'