Hello!
I have problem on Debian 12. When I try linking simple program with SDL2 library i have error:

/usr/bin/ld: /tmp/cc6bgbfu.o: in function `main':
sdl_test.cpp.text+0x15): undefined reference to `SDL_Init'
collect2: error: ld returned 1 exit status

I have no idea why i cant linking with SDL2.

Simple main:

#include <SDL2/SDL.h>

auto main(int argc, char** argv) -> int {
SDL_Init(SDL_INIT_EVERYTHING);
return (0);
}

Can some one answer my why i have error ? Library is installed :

ls /usr/lib/x86_64-linux-gnu/ | grep libSDL*
libSDL2-2.0.so
libSDL2-2.0.so.0
libSDL2-2.0.so.0.2600.5
libSDL2.a
libSDL2main.a
libSDL2.so
libSDL2_test.a

Il try send to g++ different options with path, using sdl-config, etc..

Thank You for answer.

You do have to link the library when linking your program : -lSDL2main -lSDL2

1 members found this post helpful.

Also: most often, these "arcane things that you have to include on a command-line" are instead incorporated into a Makefile. Nearly every project has one. So that all you have to do, to prepare your project to run, is to type the single command: make.

This command, first, determines "which source-files need to be recompiled," then automatically does it. Then, it figures out how to link everything together, and does it. Poof. And this magic is accomplished by the "Makefile," which is part of the project.

Surf out to sites such as "GitHub" and "SourceForge" to locate projects which also use the libraries that you are interested in using. See how they did it.

Here is a link to one such reference on the make file. Lazy Foo SDL tutorial

Im linking with all libraries:
g++ -lSDL2 -lSDL2main sdl_test.cpp
/usr/bin/ld: /tmp/cc5ms8uK.o: in function `main':
sdl_test.cpp.text+0x15): undefined reference to `SDL_Init'
collect2: error: ld returned 1 exit status

Put the libraries AFTER the .cpp file(s).

g++ sdl_test.cpp -lSDL2main -lSDL2

Here is a sample makefile (note I didn't have to use SDL2main library to run, and it was a work in progress, but runs fine )

The order matters:

Really Thanks. But i don't know why libraries must be AFTER .cpp files.
BTW thanks again .

Well, in simple terms, the linker will not include functions from a library if no functions are used from it. So when you place libraries before your source files, it thinks that nothing is used from the library (nothing in the symbol table yet) and drops them. This causes your error once the source (*.cpp) files are loaded and linker finds missing symbol references. That is why 'order' matters.

1 members found this post helpful.

It's the way the linker works: it uses libraries to fill the holes in the things that have come before. Anything that comes after the library won't have its holes filled¹

____
1) Oooh Er, Missus! That sentence ended up sounding much ruder than I intended.

Admittedly, this command-line behavior is counter-intuitive. (You would “reasonably expect” it to process all the files first, then all the libraries.)

This is a great argument for building a “Makefile,” and for trolling sites such as GitHub and SourceForge, looking for projects similar to yours and “cabbaging” Arcane Wisdoms from their Makefiles. (Why pound your head against obscurities like these, when somebody else out there already did?)

Also: there are “Makefile generators.” People have indeed addressed the various deficiencies of the original system.