Merging Jar Files (Or a ZIP with a Jar) in C++

I have a jar file and a zip file. I need to move the contents of the .zip into the .jar--how can I do this using C++? I have no pre-existing code, and no idea where to begin. Any help would be greatly appreciated.

The application of this is with a custom Minecraft launcher. I need to merge the forge files with the Minecraft.jar file. Its illegal to distribute a modded Minecraft.jar--Gotta download the normal one from Minecraft, then the mods, and then combine.

Thanks!