Strange SDL getAttribute() behaviour - opengl

Question

I instructed SDL to use at least 8 bits for the stencil buffer:
if (SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 8) < 0)
{
printf("couldn't set stencil size: %s\n", SDL_GetError());
}
That works because it gives no error.
But later in the code, I try to get the stencil size value:
int rc, i;
rc = SDL_GL_GetAttribute(SDL_GL_STENCIL_SIZE, &i);
printf("stencil buffer size: (returns %i):%i sdl-error:%s\n", rc, i, SDL_GetError());
That returns -1, and outputs this:
stencil buffer size: (returns -1):0 sdl-error:OpenGL error: GL_INVALID_ENUM
If cleared any SDL error using SDL_ClearError(), so this must be the reason. But I have no idea why.
Maybe there might be a bigger error, since glGetError() returns GL_INVALID_ENUM right after GLEW initialization, the same error as SDL gives.
Note: Thanks #Nicol Bolas, I edited the wrong call.
EDIT:
I tried to change the context version, and the greatest version which works, is 3.1, glew generates no error, and sdl returns 8 as stencil size.
But why? I read the GLEW changelog, and it says, that my glew version (1.13.0) should be able to handle opengl 4: http://glew.sourceforge.net/
So, what's wrong?

Answer 1

Since the stencil stuff works now, I just cleared the error generated by GLEW by calling glGetError(). For those who are interested, here is paragraph concerning the error: (link:https://www.opengl.org/wiki/OpenGL_Loading_Library)
GLEW has a problem with core contexts. It calls glGetString(GL_EXTENSIONS)​, which causes GL_INVALID_ENUM on GL 3.2+ core context as soon as glewInit()​ is called. It also doesn't fetch the function pointers. The solution is for GLEW to use glGetStringi​ instead. The current version of GLEW is 1.10.0 but they still haven't corrected it. The only fix is to use glewExperimental​ for now.glewExperimental​ is a variable that is already defined by GLEW. You must set it to GL_TRUE before calling glewInit()​. You might still get GL_INVALID_ENUM (depending on the version of GLEW you use), but at least GLEW ignores glGetString(GL_EXTENSIONS)​ and gets all function pointers.