# Compile error: undefined reference to class constructor even though it is included

**URL:** <https://discourse.cmake.org/t/compile-error-undefined-reference-to-class-constructor-even-though-it-is-included/5761>\
**Category:** Code\
**Tags:** os:windows\
**Created:** [May 30, 2022, 5:58pm UTC](https://discourse.cmake.org/t/compile-error-undefined-reference-to-class-constructor-even-though-it-is-included/5761 "2022-05-30T17:58:20Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![Coziyu](https://discourse.cmake.org/user_avatar/discourse.cmake.org/coziyu/32/2438_2.png) [@Coziyu](https://discourse.cmake.org/u/Coziyu)\
**Post date:** [May 30, 2022, 5:58pm UTC](https://discourse.cmake.org/t/compile-error-undefined-reference-to-class-constructor-even-though-it-is-included/5761/1 "2022-05-30T17:58:20Z")

</div>

Hey there!  
I am a beginner learning how to use CMake in my VSCode C++ projects and I’m having some issues getting my code to compile properly. Intellisense doesn’t give me any errors.

When using CMake to build my project, it throws the following error: `D:/Code/Projects/LearnOpenGL/src/main.cpp:34: undefined reference to `Shader::Shader(char const*, char const*)'` This Shader class is declared in `shader.h` and defined in `shader.cpp`

After searching online, I found that including `shader.cpp` allows me to compile the file without issue. Is there something wrong with my CMakeLists.txt file to make it unable to be compiled?

Here is my project file structure:

```auto
TestProject
||.vscode
||build
||||autogenerated stuff here
||include
||||glad
||||||glad.h
||||GLFW
||||||glfw3.h
||||headers
||||||data.h
||||||func.h
||||||shader.h
||src
||main.cpp
||glad.c
||funcs
||||data.cpp
||||func.cpp
||||shader.cpp
||CMakeLists.txt

```

Here is my `main.cpp`

```auto
#include <iostream>
#include <fstream>
#include <streambuf>
#include <cmath>
#include <glad\glad.h>
#include <GLFW\glfw3.h>
#include "headers/func.h"
#include "headers/data.h"
#include "headers/shader.h"

int main(){

    ......
    Shader myShader("./shaders/vertexShader1.vert","./shaders/fragmentShader1.frag");

    while(!glfwWindowShouldClose(window)){
        ......
        myShader.use();
    }
    ......
    return 0; 
}

```

Here is my `shader.h`

```auto
#pragma once

#include <glad/glad.h> // include glad to get all the required OpenGL headers
#include <string>
#include <fstream>
#include <sstream>
#include <iostream>

class Shader
{
public:
    // the program ID
    unsigned int ID;
  
    // constructor reads and builds the shader
    Shader(const char* vertexPath, const char* fragmentPath);
    // use/activate the shader
    void use();
    // utility uniform functions
    void setBool(const std::string &name, bool value) const;  
    void setInt(const std::string &name, int value) const;   
    void setFloat(const std::string &name, float value) const;
};
  

```

Here is my `shader.cpp`

```auto
#include <glad/glad.h> // include glad to get all the required OpenGL headers
#include <string>
#include <fstream>
#include <sstream>
#include <iostream>
class Shader
{
public:
    unsigned int ID;

    Shader(const char* vertexPath, const char* fragmentPath){
        ......
        //generates shaders from text here
    }

    void use(){
        ......
    }

    void setBool(const std::string &name, bool value) const{         
        ......
    }
    void setInt(const std::string &name, int value) const{ 
        ......
    }
    void setFloat(const std::string &name, float value) const{ 
        ......
    } 
};

```

Here is my `CMakeLists.txt`

```auto
cmake_minimum_required(VERSION 3.0.0)
project(rendering VERSION 0.1.0)

include_directories("${CMAKE_SOURCE_DIR}\\include")
set(CMAKE_PREFIX_PATH "${CMAKE_SOURCE_DIR}")

set(CMAKE_CXX_STANDARD_LIBRARIES "-static-libgcc -static-libstdc++ -lwsock32 -lws2_32 ${CMAKE_CXX_STANDARD_LIBRARIES}")
set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -Wl,-Bstatic,--whole-archive -lwinpthread -Wl,--no-whole-archive")

set(HEADER_FILES 
include/headers/data.h
include/headers/func.h
include/headers/shader.h
include/glad/glad.h
)

set(SOURCE 
src/main.cpp
src/funcs/func.cpp
src/funcs/data.cpp
src/funcs/shader.cpp
)

set(LIBRARY 
OpenGL::GL
glad
glfw
)

find_package(OpenGL REQUIRED)
find_package(glfw3 REQUIRED)

add_library(glad STATIC src/glad.c)
add_executable(rendering "${SOURCE}")
#//target_include_directories(rendering PUBLIC "${CMAKE_SOURCE_DIR}\\include") #UNSURE WHETHER NEEDED
target_link_libraries(rendering "${LIBRARY}")

```

Thanks very much for reading!

---

<div class="post-metadata">

**Author:** ![ben.boeckel](https://discourse.cmake.org/letter_avatar_proxy/v4/letter/b/ea5d25/32.png) [@ben.boeckel](https://discourse.cmake.org/u/ben.boeckel)\
**Post date:** [May 30, 2022, 7:30pm UTC](https://discourse.cmake.org/t/compile-error-undefined-reference-to-class-constructor-even-though-it-is-included/5761/2 "2022-05-30T19:30:30Z")

</div>

> [@Coziyu](#):
>
> Here is my `shader.cpp`

You are redeclaring `Shader` in this file. You define declared class members with `Shader::` in this instance:

```cxx
Shader::Shader(const char*, const char*)
{
    // …
}

```

---

<div class="post-metadata">

**Author:** ![Coziyu](https://discourse.cmake.org/user_avatar/discourse.cmake.org/coziyu/32/2438_2.png) [@Coziyu](https://discourse.cmake.org/u/Coziyu)\
**Post date:** [May 31, 2022, 2:21am UTC](https://discourse.cmake.org/t/compile-error-undefined-reference-to-class-constructor-even-though-it-is-included/5761/3 "2022-05-31T02:21:18Z")

</div>

Oh my, that’s a silly mistake I made.

Thank you very much for your help!