How to statically link a library to another library with all symbols resolved

Question

I have some XML parsing utility functions written inside C headers and source files based on expat library. For this I have compiled my source files to a static library with expat statically linked to it.

I am able to use and the functions from the resulting xml utilities library with my applications only if I statically link both the utility library and expat with my application. I was of the view that I should be able to get my application built with only statically linking my utility library without requiring to statically link expat again with the application executable. Only linking my application with the utility library gives undefined symbol error for expat.

Can someone please guide me what am I missing ? I am using gcc compiler.

Thanks....

Answer 1

"I have compiled my source files to a static library with expat statically linked to it."

I'm fraid you haven't. A static library is not produced by the linker; no linkage is involved, so nothing can be linked to it. A static library is nothing but a bag of object files in ar archive format. When you are linking something that is produced by the linker - namely a program or a shared library - you may offer such a bag to the linker. It will look in the bag and take out just the object files it needs to carry on the linkage and link them into the target. The bag spares you the difficulty of needing to know exactly which of the object files in it the linker will need, but the bag itself contributes nothing at all to the linkage.

Later

How can I get expat static library included in my utilities library, so that I only need to link my executable with a single static library. I don't want to extract the two archives and merge the object files together.

There is no other way of combining two ar archives.

Your resistance to linking libexpat is puzzling, without further context. It is available through the package manager on any distro. You've made a library that depends on libexpat. Clients that link your library will need also need to link libexpat. This is an utterly routine sort of dependency that you should simply document and - if you are packaging your library - include in the package dependencies. Almost invariably when we write new libraries we are augmenting the libraries already available to our target users. If every library statically incorporated all of its own dependencies then they would all be the size of an operating system and of no practical use.