OpenGL / MinGW: undefined reference to 'glGetString' - solution

[artganseforth]

Hi All,

if you get linker-errors with MinGW concerning 'glGetStrig' or 'glGetSring@4' etc., inserting the followinng codeline somewhere in OpenGL initialisation might help:

const GLubyte* dummy = glGetString(1);

Note: 'glGetStrig' is also called by some library-functions. So this error may appear without any 'glGetStrig'-call in your own code.


Greetz,
FG.

[coder777]

Linker error cannot be solved by a function call. You need to provide the correct libraries to the linker. Why do you think that could help?

[artganseforth]

Hi coder777,

you're right, this is absolutly strange, but for me it was even more strange, that a library-function which is not called by my program-code, causes linking-problems. For me this meaned that there is something wrong with the inner dependencies of the library.
In fact this is why i found this 'solution': I alway got 'glGetString'-linking-errors at a code where i was sure that it shold work and somehow i figured out, that a call of 'glGenFramebuffer' or 'glBindFramebuffer' causes them. This was so strange, that i wanted to find out, what happens if i call 'glGetString' directly. And - uups - suddenly also the 'gl...Framebuffer'-call was compiled correctly.

I don't know why, but i had this problem in two programs now and both times it worked.

Maybe it has to do something with compiler-heuristics, like this: in some cases with MinGW an object, need an expicit destructor in the .c file to be linkable. A destructor-function in the object-protoype (something like "~Name() {..};") leads to 'undefined reference to'-errors. With any other function (incuding the constructor) this causes no problem. So obviously the compiler needs the destuctor as 'hook' for the linking-table-entry. This might be some simelar thing...

Regards,
F

[coder777]

It sounds like as if you provide multiple conflicting [version] librarys. When you add that particular line the linker accidentally chooses the right one. If so this behavior might even change the next time you change your code.

[artganseforth]

There you migth be right. I'm not good in setting up c-compilers and the result is more accidetially then planned. But this is the second independent compiler-setup, where this appers. So i obviously installed accidentially two tlimes the same incompatible librarys.

In fact - which is quiet funny - yesterday i had this problem and it was my own forgotton post from 2014 (http://www.cplusplus.com/forum/general/142808/) i found on google, which helped me this time.
So i thought, it will be good to make a second post for other people.

By the way: also if libraries don't fit, this behaviour is quiet strange, isn't it??