Node:Archive Suffix Rules, Previous:Archive Pitfalls, Up:Archives

### Suffix Rules for Archive Files

You can write a special kind of suffix rule for dealing with archive files. See Suffix Rules, for a full explanation of suffix rules. Archive suffix rules are obsolete in GNU `make`, because pattern rules for archives are a more general mechanism (see Archive Update). But they are retained for compatibility with other `make`s.

To write a suffix rule for archives, you simply write a suffix rule using the target suffix `.a` (the usual suffix for archive files). For example, here is the old-fashioned suffix rule to update a library archive from C source files:

         .c.a:
                 $(CC) $(CFLAGS) $(CPPFLAGS) -c $< -o $*.o
                 $(AR) r $@ $*.o
                 $(RM) $*.o

This works just as if you had written the pattern rule:

         (%.o): %.c
                 $(CC) $(CFLAGS) $(CPPFLAGS) -c $< -o $*.o
                 $(AR) r $@ $*.o
                 $(RM) $*.o

In fact, this is just what `make` does when it sees a suffix rule with `.a` as the target suffix. Any double-suffix rule `.`x`.a` is converted to a pattern rule with the target pattern `(%.o)` and a prerequisite pattern of `%.`x``.

Since you might want to use `.a` as the suffix for some other kind of file, `make` also converts archive suffix rules to pattern rules in the normal way (see Suffix Rules). Thus a double-suffix rule `.`x`.a` produces two pattern rules: `(%.o): %.`x`` and `%.a: %.`x``.