Error when Including Header File Utils.h : Undefined Reference `Utils::createShaderProgram`

Question

I want to show a green cube, in a directory there are .cpp, .h, and .glsl files:

1. main.cpp
2. Utils.h
3. vertShader.glsl
4. fragShader.glsl

I want to compile it using CMakeLists.txt:

cmake_minimum_required(VERSION 3.17)

project(test LANGUAGES CXX)

add_executable(test main.cpp)
target_link_libraries(test GLEW GL glfw )
target_include_directories(test PUBLIC /root/SourceCodes/CPP/include/)

(I put the Utils.h in the /root/SourceCodes/CPP/include/ as well)

But, the problem is I get error: Undefined Reference Utils::createShaderProgram

the codes / MWE for the files above:

main.cpp

#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <string>
#include <iostream>
#include <fstream>
#include <cmath>
#include <glm/glm.hpp>
#include <glm/gtc/type_ptr.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include "Utils.h"

using namespace std;

#define numVAOs 1
#define numVBOs 2

float cameraX, cameraY, cameraZ;
float cubeLocX, cubeLocY, cubeLocZ;
GLuint renderingProgram;
GLuint vao[numVAOs];
GLuint vbo[numVBOs];

GLuint mvLoc, projLoc;
int width, height;
float aspect;
glm::mat4 pMat, vMat, mMat, mvMat;

void setupVertices(void) { // 36 vertices, 12 triangles, makes 2x2x2 cube placed at origin
    float vertexPositions[108] = {
    -1.0f, 1.0f, -1.0f, -1.0f, -1.0f, -1.0f, 1.0f, -1.0f, -1.0f,
    1.0f, -1.0f, -1.0f, 1.0f, 1.0f, -1.0f, -1.0f, 1.0f, -1.0f,
    1.0f, -1.0f, -1.0f, 1.0f, -1.0f, 1.0f, 1.0f, 1.0f, -1.0f,
    1.0f, -1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, -1.0f,
    1.0f, -1.0f, -1.0f, 1.0f, -1.0f, 1.0f, 1.0f, 1.0f, 1.0f,
    -1.0f, -1.0f, 1.0f, -1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f,
    -1.0f, -1.0f, 1.0f, -1.0f, -1.0f, -1.0f, -1.0f, 1.0f, 1.0f,
    -1.0f, -1.0f, -1.0f, -1.0f, 1.0f, -1.0f, -1.0f, 1.0f, 1.0f,
    -1.0f, -1.0f, 1.0f, -1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f,
    1.0f, -1.0f, -1.0f, -1.0f, -1.0f, -1.0f, -1.0f, -1.0f, 1.0f,
    -1.0f, 1.0f, -1.0f, 1.0f, 1.0f, -1.0f, 1.0f, 1.0f, 1.0f,
    1.0f, 1.0f, 1.0f, -1.0f, 1.0f, 1.0f, -1.0f, 1.0f, -1.0f,
    };
    glGenVertexArrays(1,vao);
    glBindVertexArray(vao[0]);
    glGenBuffers(numVBOs, vbo);

    glBindBuffer(GL_ARRAY_BUFFER, vbo[0]);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertexPositions), vertexPositions, GL_STATIC_DRAW);
}

void init(GLFWwindow* window){
    
    // Utils
    renderingProgram = Utils::createShaderProgram(
        "vertShader.glsl",
        "fragShader.glsl");
    cubeLocX = 0.0f; cubeLocY = -2.0f; cubeLocZ = 0.0f;
    setupVertices();
}

void display(GLFWwindow* window, double currentTime) {
    glClear(GL_DEPTH_BUFFER_BIT);
    glUseProgram(renderingProgram);
    
    // get the uniform variables for the MV and projection matrices
    mvLoc = glGetUniformLocation(renderingProgram, "mv_matrix");
    projLoc = glGetUniformLocation(renderingProgram, "proj_matrix");

    // build perspective matrix
    glfwGetFramebufferSize(window, &width, &height);
    aspect = (float)width / (float)height;
    pMat = glm::perspective(1.0472f, aspect, 0.1f, 1000.0f); // 1.0472 radians = 60 degrees

    // build view matrix, model matrix, and model-view matrix
    vMat = glm::translate(glm::mat4(1.0f), glm::vec3(-cameraX, -cameraY, -cameraZ));
    mMat = glm::translate(glm::mat4(1.0f), glm::vec3(cubeLocX, cubeLocY, -cubeLocZ));
    mvMat = vMat * mMat;

    // copy perspective and MV matrices to corresponding uniform variables
    glUniformMatrix4fv(mvLoc, 1, GL_FALSE, glm::value_ptr(mvMat));
    glUniformMatrix4fv(projLoc, 1, GL_FALSE, glm::value_ptr(pMat));

    // associate VBO with the corresponding vertex attribute in the vertex shader
    glBindBuffer(GL_ARRAY_BUFFER, vbo[0]);
    glVertexAttribPointer(0,3, GL_FLOAT, GL_FALSE, 0, 0);
    glEnableVertexAttribArray(0);
    
    // adjust OpenGL settings and draw model
    glEnable(GL_DEPTH_TEST);
    glDepthFunc(GL_LEQUAL);
    glDrawArrays(GL_TRIANGLES,0,36);
}

int main(void)
{
    glfwInit(); //initialize GLFW and GLEW libraries
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    
    GLFWwindow* window = glfwCreateWindow(600, 600, " Learn Open GL with GLFW: Green Cube", NULL, NULL);
    glfwMakeContextCurrent(window);
    if(glewInit() != GLEW_OK) {
        exit(EXIT_FAILURE); 
    }
    glfwSwapInterval(1);
    
    init(window);
    
    while(!glfwWindowShouldClose(window)) {
        display(window, glfwGetTime());
        glfwSwapBuffers(window);
        glfwPollEvents();
    }
    glfwDestroyWindow(window);
    glfwTerminate();
    exit(EXIT_SUCCESS); 
    //return 0;
}

Utils.h

#include <GL/glew.h>
#include <GLFW/glfw3.h>
//#include <SOIL2/SOIL2.h>
#include <string>
#include <iostream>
#include <fstream>
#include <cmath>
#include <vector>
#include <glm/glm.hpp>
#include <glm/gtc/type_ptr.hpp>
#include <glm/gtc/matrix_transform.hpp>

class Utils
{
private:
    static std::string readShaderFile(const char *filePath);
    static void printShaderLog(GLuint shader);
    static void printProgramLog(int prog);
    static GLuint prepareShader(int shaderTYPE, const char *shaderPath);
    static int finalizeShaderProgram(GLuint sprogram);

public:
    Utils();
    static bool checkOpenGLError();
    static GLuint createShaderProgram(const char *vp, const char *fp);
    static GLuint createShaderProgram(const char *vp, const char *gp, const char *fp);
    static GLuint createShaderProgram(const char *vp, const char *tCS, const char* tES, const char *fp);
    static GLuint createShaderProgram(const char *vp, const char *tCS, const char* tES, char *gp, const char *fp);
    static GLuint loadTexture(const char *texImagePath);
    static GLuint loadCubeMap(const char *mapDir);

    static float* goldAmbient();
    static float* goldDiffuse();
    static float* goldSpecular();
    static float goldShininess();

    static float* silverAmbient();
    static float* silverDiffuse();
    static float* silverSpecular();
    static float silverShininess();

    static float* bronzeAmbient();
    static float* bronzeDiffuse();
    static float* bronzeSpecular();
    static float bronzeShininess();
};

fragShader.glsl

#version 330

out vec4 color;

uniform mat4 mv_matrix;
uniform mat4 proj_matrix;

void main(void) {
    color = vec4(0.0, 1.0, 0.0, 1.0);
}

vertShader.glsl

#version 330

layout (location=0) in vec3 position;

uniform mat4 mv_matrix;
uniform mat4 proj_matrix;

void main(void) {
    gl_position = proj_matrix * mv_matrix * vec4(position, 1.0);
}