Not sure if this is the problem, but I'll post my opengl version on linux anyways.

Code :
 glxinfo | grep 'version'
server glx version string: 1.4
client glx version string: 1.4
GLX version: 1.4
    Max core profile version: 3.3
    Max compat profile version: 3.0
    Max GLES1 profile version: 1.1
    Max GLES[23] profile version: 3.0
OpenGL core profile version string: 3.3 (Core Profile) Mesa 17.2.4
OpenGL core profile shading language version string: 3.30
OpenGL version string: 3.0 Mesa 17.2.4
OpenGL shading language version string: 1.30
OpenGL ES profile version string: OpenGL ES 3.0 Mesa 17.2.4
OpenGL ES profile shading language version string: OpenGL ES GLSL ES 3.00


Anyways I'm following the tutorial on this page https://open.gl/feedback and my output is a string of zero's instead of the
normal square roots of 1 to 5. Here's the code; it compiles with these libs in codeblocks

-lGL
-lGLU
-lGLEW
-lsfml-graphics
-lsfml-window
-lsfml-system

Here's the code

Code :
 
 
// Link statically with GLEW
#define GLEW_STATIC
 
// Headers
#include <GL/glew.h>
#include <SFML/Window.hpp>
 
// Vertex shader
const GLchar* vertexShaderSrc = R"glsl(        in float inValue;    out float geoValue;    void main()    {        geoValue = sqrt(inValue);    } )glsl";
 
// Geometry shader
const GLchar* geoShaderSrc = R"glsl(        layout(points) in;    layout(triangle_strip, max_vertices = 3) out;    in float[] geoValue;    out float outValue;    void main()    {        for (int i = 0; i < 3; i++)        {            outValue = geoValue[0] + i;            EmitVertex();        }        EndPrimitive();    } )glsl";
 
int main()
{
    sf::ContextSettings settings;
    settings.depthBits = 24;
    settings.stencilBits = 8;
 
    sf::Window window(sf::VideoMode(800, 600, 32), "Transform Feedback", sf::Style::Titlebar | sf::Style::Close, settings);
 
    // Initialize GLEW
    glewExperimental = GL_TRUE;
    glewInit();
 
    // Compile shaders
    GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexShaderSrc, nullptr);
    glCompileShader(vertexShader);
 
    GLuint geoShader = glCreateShader(GL_GEOMETRY_SHADER);
    glShaderSource(geoShader, 1, &geoShaderSrc, nullptr);
    glCompileShader(geoShader);
 
    // Create program and specify transform feedback variables
    GLuint program = glCreateProgram();
    glAttachShader(program, vertexShader);
    glAttachShader(program, geoShader);
 
    const GLchar* feedbackVaryings[] = { "outValue" };
    glTransformFeedbackVaryings(program, 1, feedbackVaryings, GL_INTERLEAVED_ATTRIBS);
 
    glLinkProgram(program);
    glUseProgram(program);
 
    // Create VAO
    GLuint vao;
    glGenVertexArrays(1, &vao);
    glBindVertexArray(vao);
 
    // Create input VBO and vertex format
    GLfloat data[] = { 1.0f, 2.0f, 3.0f, 4.0f, 5.0f };
 
    GLuint vbo;
    glGenBuffers(1, &vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(data), data, GL_STATIC_DRAW);
 
    GLint inputAttrib = glGetAttribLocation(program, "inValue");
    glEnableVertexAttribArray(inputAttrib);
    glVertexAttribPointer(inputAttrib, 1, GL_FLOAT, GL_FALSE, 0, 0);
 
    // Create transform feedback buffer
    GLuint tbo;
    glGenBuffers(1, &tbo);
    glBindBuffer(GL_ARRAY_BUFFER, tbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(data) * 3, nullptr, GL_STATIC_READ);
 
    // Perform feedback transform
    glEnable(GL_RASTERIZER_DISCARD);
 
    glBindBufferBase(GL_TRANSFORM_FEEDBACK_BUFFER, 0, tbo);
 
    glBeginTransformFeedback(GL_TRIANGLES);
        glDrawArrays(GL_POINTS, 0, 5);
    glEndTransformFeedback();
 
    glDisable(GL_RASTERIZER_DISCARD);
 
    glFlush();
 
    // Fetch and print results
    GLfloat feedback[15];
    glGetBufferSubData(GL_TRANSFORM_FEEDBACK_BUFFER, 0, sizeof(feedback), feedback);
 
    for (int i = 0; i < 15; i++)
    {
        printf("%f\n", feedback[i]);
    }
 
    glDeleteProgram(program);
    glDeleteShader(geoShader);
    glDeleteShader(vertexShader);
 
    glDeleteBuffers(1, &tbo);
    glDeleteBuffers(1, &vbo);
 
    glDeleteVertexArrays(1, &vao);
 
    window.close();
 
    return 0;
}


I removed the version numbers from the shaders as neither 150 or 130 work. thanks ahead!