GCC, stringification, and inline GLSL?

Unfortunately, having preprocessor directives in the argument of a macro is undefined, so you can't do this directly. But as long as none of your shaders need preprocessor directives other than #version, you could do something like:

#define GLSL(version, shader)  "#version " #version "\n" #shader

const GLchar* vert = GLSL(120,
    attribute vec2 position;
    void main()
    {
        gl_Position = vec4( position, 0.0, 1.0 );
    }
);

To achieve this purpose I used sed. I have seperate files with GLSL which I edit (with proper syntax highlighting), and in the same time GLSL in inlined in C++. Not very cross platform, but with msys it works under windows.

In C++ code:

const GLchar* vert = 
#include "shader_processed.vert"
;

In Makefile:

shader_processed.vert: shader.vert
    sed -f shader.sed shader.vert > shader_processed.vert

programm: shader_processed.vert main.cpp
    g++ ...

shader.sed

s|\\|\\\\|g
s|"|\\"|g
s|$|\\n"|g
s|^|"|g

Can you use C++11? If so you could use raw string literals:

const GLchar* vert = R"END(
#version 120
attribute vec2 position;
void main()
{
    gl_Position = vec4( position, 0.0, 1.0 );
}
)END";

No need for escapes or explicit newlines. These strings start with an R (or r). You need a delimiter (I chose END) between the quote and the first parenthesis to escape parenthesis which you have in the code snippet.