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Building etags and ctags

Here is another, trickier example. It shows how to generate two programs (ctags and etags) from the same source file (`etags.c'). The difficult part is that each compilation of `etags.c' requires different cpp flags.

bin_PROGRAMS = etags ctags
ctags_SOURCES =
ctags_LDADD = ctags.o

etags.o: etags.c
        $(COMPILE) -DETAGS_REGEXPS -c etags.c

ctags.o: etags.c
        $(COMPILE) -DCTAGS -o ctags.o -c etags.c

Note that ctags_SOURCES is defined to be empty--that way no implicit value is substituted. The implicit value, however, is used to generate etags from `etags.o'.

ctags_LDADD is used to get `ctags.o' into the link line. ctags_DEPENDENCIES is generated by Automake.

The above rules won't work if your compiler doesn't accept both `-c' and `-o'. The simplest fix for this is to introduce a bogus dependency (to avoid problems with a parallel make):

etags.o: etags.c ctags.o
        $(COMPILE) -DETAGS_REGEXPS -c etags.c

ctags.o: etags.c
        $(COMPILE) -DCTAGS -c etags.c && mv etags.o ctags.o

Also, these explicit rules do not work if the de-ANSI-fication feature is used (see section Automatic de-ANSI-fication). Supporting de-ANSI-fication requires a little more work:

etags._o: etags._c ctags.o
        $(COMPILE) -DETAGS_REGEXPS -c etags.c

ctags._o: etags._c
        $(COMPILE) -DCTAGS -c etags.c && mv etags._o ctags.o

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