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?

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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.

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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.