question about compiled program usage of external libraries

Question

I know this might be a very stupid question but I am new to compiled languages (my domain is mostly scripting languages like PHP, Python or JavaScript).

I am learning C++ for one project where it is the only language I can use.

I wrote a program in Ubuntu 10.10 and then compiled it. I can run the generated binary file from cmd like this and it works:

sudo ./compiled-program

But, I have used some external libraries in the program (OpenCV). Does that mean that all computers where I will run the program will have to have OpenCV installed? Or is OpenCV bundled inside the compiled binary file? Will it work on PCs without OpenCV installed?

Answer 1

You should read a few things about libraries, and particularly what makes the difference between static and dynamic libraries. To quote the basic definitions so you get the point :

A static library, also known as an archive, consists of a set of routines which are copied into a target application by the compiler, linker, or binder, producing object files and a stand-alone executable file.

[...]

Dynamic linking involves loading the subroutines of a library (which may be referred to as a DLL, especially under Windows, or as a DSO (dynamic shared object) under Unix-like systems) into an application program at load time or runtime, rather than linking them in at compile time.

Answer 2

Not a stupid question at all!

The "normal" way this works - is that your program has been linked against a "Shared Library" - in which case, yes, the user needs the OpenCV (or whatever bundle includes the shared library) to work.

If you compiled as a static executable, (using the -static) flag, then it, and all libraries would be included directly into your executable, making a bit of a larger executable that wastes more memory, because it isn't using a shared library.

There are ways that you could compile your program to link only your OpenCV libraries as static - but that only can be done if the bundle included a static library ".a" vs. a shared one ".so".