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11.2 Implicit Rule for Archive Member Targets
Recall that a target that looks like ‘a(m)’ stands for the member named m in the archive file a.
When make
looks for an implicit rule for such a target, as a special
feature it considers implicit rules that match ‘(m)’, as well as
those that match the actual target ‘a(m)’.
This causes one special rule whose target is ‘(%)’ to match. This rule updates the target ‘a(m)’ by copying the file m into the archive. For example, it will update the archive member target ‘foo.a(bar.o)’ by copying the file ‘bar.o’ into the archive ‘foo.a’ as a member named ‘bar.o’.
When this rule is chained with others, the result is very powerful. Thus, ‘make "foo.a(bar.o)"’ (the quotes are needed to protect the ‘(’ and ‘)’ from being interpreted specially by the shell) in the presence of a file ‘bar.c’ is enough to cause the following recipe to be run, even without a makefile:
cc -c bar.c -o bar.o ar r foo.a bar.o rm -f bar.o
Here make
has envisioned the file ‘bar.o’ as an intermediate
file. See section Chains of Implicit Rules.
Implicit rules such as this one are written using the automatic variable ‘$%’. See section Automatic Variables.
An archive member name in an archive cannot contain a directory name, but
it may be useful in a makefile to pretend that it does. If you write an
archive member target ‘foo.a(dir/file.o)’, make
will perform
automatic updating with this recipe:
ar r foo.a dir/file.o
which has the effect of copying the file ‘dir/file.o’ into a member
named ‘file.o’. In connection with such usage, the automatic variables
%D
and %F
may be useful.
11.2.1 Updating Archive Symbol Directories | How to update archive symbol directories. |
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