SDL_GL_SetAttribute (3)

#include "SDL.h"

int SDL_GL_SetAttribute(SDL_GLattr attr, int value);

Sets the OpenGL attribute attr to value. The attributes you set don't take effect until after a call to SDL_SetVideoMode. You should use SDL_GL_GetAttribute to check the values after a SDL_SetVideoMode call.

Returns 0 on success, or -1 on error.

SDL_GL_SetAttribute( SDL_GL_RED_SIZE, 5 );
SDL_GL_SetAttribute( SDL_GL_GREEN_SIZE, 5 );
SDL_GL_SetAttribute( SDL_GL_BLUE_SIZE, 5 );
SDL_GL_SetAttribute( SDL_GL_DEPTH_SIZE, 16 );
SDL_GL_SetAttribute( SDL_GL_DOUBLEBUFFER, 1 );
if ( (screen=SDL_SetVideoMode( 640, 480, 16, SDL_OPENGL )) == NULL ) {
  fprintf(stderr, "Couldn't set GL mode: %s
", SDL_GetError());
  SDL_Quit();
  return;
}

Note:

The SDL_DOUBLEBUF flag is not required to enable double buffering when setting an OpenGL video mode. Double buffering is enabled or disabled using the SDL_GL_DOUBLEBUFFER attribute.

SDL_GL_GetAttribute, GL Attributes