Autoconf, Automake, and Libtool: Automatic dependency tracking

| ## 19.3 Automatic dependency tracking Keeping track of dependencies for a large program is tedious and error-prone. Many edits require the programmer to update dependencies, but for some changes, such as adding a `#include` to an existing header, the change is large enough that he simply refuses (or does it incorrectly). To fix this problem, Automake supports automatic dependency tracking. The implementation of automatic dependency tracking in Automake 1.4 requires `gcc` and GNU `make`. These programs are only required for maintainers; the ``Makefile'`s generated by `make dist` are completely portable. If you can't use `gcc` or GNU `make` for your project, then you are simply out of luck; you have to disable dependency tracking. Automake 1.5 will include a completely new dependency tracking implementation. This new implementation will work with any compiler and any version of `make`. Another limitation of the current scheme is that the dependencies included into the portable ``Makefile'`s by `make dist` are derived from the current build environment. First, this means that you must use `make all` before you can meaningfully run `make dist` (otherwise the dependencies won't have been created). Second, this means that any files not built in your current tree will not have dependencies in the distributed ``Makefile'`s. The new implementation will avoid both of these shortcomings as well. Automatic dependency tracking is on by default; you don't have to do anything special to get it. To turn it off, either run `automake -i` instead of plain `automake`, or put ``no-dependencies'` into the ``AUTOMAKE_OPTIONS'` macro in each ``Makefile.am'`.

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