Runtime dependency and build dependency concepts

Question

I have been hearing about build dependency / runtime dependency. They are quite self explanatory terms. As far as I understand, build dependency is used for components required in the compile time. For example if A has a build dependency to B, A cannot be built without B. Runtime dependency on the other hand is dynamic. If A has a runtime dependency to B, A can be built without B but cannot run without B.
This information however is too shallow. I'd like to read and understand these concepts better. I have been googling but could not find a source, can you please provide me a link or right keywords to search?

Answer 1

I'll try to keep it simple and theoretical only.

When you write code that calls function "func", compiler needs your function descriptor (e.g. "int func(char c);" usually available in .h files) to verify arguments correctness and linker needs your function implementation (where your actual code reside).

Operating systems provide mechanism to separate functions implementation into different compiled modules. It is usually required for

1. Better code reuse (multiple applications can use the same code, with different data context)
2. More efficient compilation (you don't need to recompile all dependency libraries)
3. Partial upgrades
4. Distribution of compiled libraries, without disclosing the source code

To support such functionality compiler is provided with function descriptors (.h files) as usual. While Linker is provided with lib files containing function stubs. Operating system is responsible to load an actual implementation file during application loading procedure (if it is not yet loaded for different application) and to map actual functions into memory of the new application.

Dynamic load functionality is extended for object oriented languages as well (C++, C#, Java and etc.)

Practical implementations are OS dependent - dynamic linking is implemented as DLL files in Windows or as SO files in Linux

Special OS dependent techniques can be used to share context (variables, objects) between different applications that uses the same dynamic library.

Meir Tseitlin