configure.in or configure.ac?

It seems that some autoconf projects use a configure.in file to generate a configure script, and so开发者_如何学Cme use configure.ac.

What is the difference/advantage between using one or the other?

Its just a matter of style. Historically autoconf files were named configure.in. Now configure.ac is the preferred naming scheme. Its also discussed in the documentation.

New projects should use configure.ac. Old projects used configure.in; if it is inconvenient to switch to the new name, they can continue to use it, but the autoconf tools will generate a warning.