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11.2.1 Updating Archive Symbol Directories

An archive file that is used as a library usually contains a special member named __.SYMDEF that contains a directory of the external symbol names defined by all the other members. After you update any other members, you need to update __.SYMDEF so that it will summarize the other members properly. This is done by running the ranlib program:

ranlib archivefile

Normally you would put this command in the rule for the archive file, and make all the members of the archive file prerequisites of that rule. For example,

libfoo.a: libfoo.a(x.o) libfoo.a(y.o) …
        ranlib libfoo.a

The effect of this is to update archive members x.o, y.o, etc., and then update the symbol directory member __.SYMDEF by running ranlib. The rules for updating the members are not shown here; most likely you can omit them and use the implicit rule which copies files into the archive, as described in the preceding section.

This is not necessary when using the GNU ar program, which updates the __.SYMDEF member automatically.