OpenGL|Clip planes|Geometry shader

Ponikarovskii

Hi everyone.
What am I using: Qt 5.11.1, MinGW 5.3, Windows 10, C++11, last version of OpenGL and GlSL
My task: I have non-solid (just surface) object, rendering by glDrawArrays, and i need to get cross-section of this object by plane. I have found ancient openGL function glClipPlane, but its not compability with VAOs and VBOs. Also Ive found out that its possible to rewrite glClipPlane via geometry shader.
My questions/problems:

Do you know other ways to realize this task?
I really dont understand, how to add geometry shader in QtCreator, there is no "icon" of geometry shader, I tried to add vertex shader and rename it to .gsh or just .glsl, tried to use QOpenGLShaderProgram::addShaderFromSourceCode(QOpenGLShader::Geometry, QString &source) and write shader code in program, but every time I get "QOpenGLShader: could not create shader" on string with adding geometry shader.
Geometry shader simpliest code:

layout (triangles) in;
layout (triangle_strip, max_vertices = 3) out;

void main()
{
    int i;

    for (i = 0; i < gl_in.length(); i++)
    {
        gl_Position = gl_in[i].gl_Position;
        EmitVertex();
    }
    EndPrimitive();
}

Im newbier in Qt, so I really need your help. Thanks.

SOLUTION
There is few ways to solve this task. You don`t need geometry shader. Just read this post on stackoverflow