Why ar gives a warning when creates a static library?

Question

I do not understand why ar gives a warning when it is creating a library.

I do this:

$ cat foo.c
int foo(int a) {
        return a + 1;
}
$ clang -c foo.c
$ ar r foo.a foo.o
ar: warning: creating foo.a
$ 

Is r the right command to use with ar? Why do I get the warning?

I am using clang and FreeBSD. Not sure if ar comes from clang or from FreeBSD.

Answer 1

If the output file doesn't already exist, you are supposed to use the c modifier. From the man page:

c

Create the archive. The specified archive is always created if it did not exist, when you request an update. But a warning is issued unless you specify in advance that you expect to create it, by using this modifier.

So try ar rc foo.a foo.o to silence the warning.