What is the difference between using `ar -rc` vs libtool?

Question

I'm new to c libraries and I'm making a project where I'm not allowed to use libtool.

I tried looking online but everything either super confusing or just how to make one with no explanation.

I have a few questions:

• Are .a libraries just a collection of .o files?
• What is the difference between using ar -rc vs libtool?
• When the linker goes to link a library does it link the whole .a file or just the part it needs?

Answer 1

Q: Are .a libraries just a collection of .o files?

A: Basically, yes.

The object files need to be organized in a specific archive library format. The linker wouldn't be able to use the archive UNLESS it recognized that format. Hence the need for tools like "ar" and "libtool".

Q: When the linker goes to link a library does it link the whole .a file or just the part it needs?*

A: Only the object code that's actually needed is physically added to the executable image.

Q: What is the difference between using ar -rc vs libtool?

"ar" has been around since the earliest days of Unix; long before "dynamic libraries" were invented (for *nix), before Linus Torvalds ever thought of Linux, or before Gnu existed. "libtool" is a Gnu tool that supports both dynamic and static libraries, and has a number of features above and beyond basic "ar" functionality.