C++ GLFW Error solved by adding legacy_stdio_definitions.lib. Why?

Question

Can anyone of you explain to me why adding "legacy_stdio_definitions.lib" resolves an error when building the following program? The error occurred when I was trying to use the GLFW library. I am still pretty new to c++ and the OpenGL world and after hours of searching online and hours of trial and error I stumbled upon the suggestion to add "legacy_stdio_definitions.lib" to my additional dependencies. This did indeed solve the error but I still don't fully understand what the problem was and what this .lib did to solve it.

I am using Microsoft Visual Studio 2015 Community Edition btw.

All the steps that i did were:

1. C/C++->General adding includes for glew, glm and glfw
2. Linker->General adding glew and glfw libs
3. Linker->Input added glew32.lib, glfw3.lib and legacy_stdio_definitions.lib
4. added glew32.dll to my project folder

---

#include <stdio.h>
#include <stdlib.h>

#include <GL/glew.h>

#include <GLFW/glfw3.h>

#include <glm/glm.hpp>
using namespace glm;

int main() {

    // Initialise GLFW
    if (!glfwInit())
    {
        fprintf(stderr, "Failed to initialize GLFW\n");
        return -1;
    }

    glfwWindowHint(GLFW_SAMPLES, 4); // 4x antialiasing
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3); // We want OpenGL 3.3
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); // To make MacOS happy; should not be needed
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE); //We don't want the old OpenGL 

                                                                   // Open a window and create its OpenGL context
    GLFWwindow* window; // (In the accompanying source code, this variable is global)
    window = glfwCreateWindow(1024, 768, "Tutorial 01", NULL, NULL);
    if (window == NULL) {
        fprintf(stderr, "Failed to open GLFW window. If you have an Intel GPU, they are not 3.3 compatible. Try the 2.1 version of the tutorials.\n");
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window); // Initialize GLEW
    glewExperimental = true; // Needed in core profile
    if (glewInit() != GLEW_OK) {
        fprintf(stderr, "Failed to initialize GLEW\n");
        return -1;
    }

    // Ensure we can capture the escape key being pressed below
    glfwSetInputMode(window, GLFW_STICKY_KEYS, GL_TRUE);

    do {
        // Draw nothing, see you in tutorial 2 !

        // Swap buffers
        glfwSwapBuffers(window);
        glfwPollEvents();

    } // Check if the ESC key was pressed or the window was closed
    while (glfwGetKey(window, GLFW_KEY_ESCAPE) != GLFW_PRESS &&
        glfwWindowShouldClose(window) == 0);

}

Any help will be appreciated.

Answer 1

Microsoft made several changes in Visual Studio 2015 that can potentially break existing codebases. Based on your description of the problem, the following is the likely culprit. Quoted from here:

The definitions of all of the printf and scanf functions have been moved inline into stdio.h, conio.h, and other CRT headers. This is a breaking change that leads to a linker error (LNK2019, unresolved external symbol) for any programs that declared these functions locally without including the appropriate CRT headers. If possible, you should update the code to include the CRT headers (that is, add #include stdio.h) and the inline functions, but if you do not want to modify your code to include these header files, an alternative solution is to add an additional library to your linker input, legacy_stdio_definitions.lib.

GLFW must have defined these functions locally without including the CRT headers.