When to Use Explicit Target Entries vs. Implicit Rules

Whenever you build a target from multiple dependency files, you must provide make with an explicit target entry that contains a rule for doing so. When building a target from a single dependency file, it is often convenient to use an implicit rule.

As the previous examples show, make readily compiles a single source file into a corresponding object file or executable. However, it has no built-in knowledge about how to link a list of object files into an executable program. Also, make compiles only those object files that it encounters in its dependency scan. It needs a starting point--a target for which each object file in the list (and ultimately, each source file) is a dependency.

So, for a target built from multiple dependency files, make needs an explicit rule that provides a collating order, along with a dependency list that accounts for its dependency files. If each of those dependency files is built from just one source, you can rely on implicit rules for them.