ImGui sample code/basic initialisation not working (Windows and Linux) - c++

Question

I am trying to setup ImGui to make some apps in, however I can't get it working. I installed the .h and .cpp files from the GitHub, https://github.com/ocornut/imgui, and followed the instructions to allow the project to compile, which it does. But on Windows and Linux (i've tried both), it spits out a runtime error, (stopped responding Windows, segmentation fault (core dumped) Linux). This is the sample code that was published,
#include "imgui.h"
int main()
{
// Create a window called "My First Tool", with a menu bar.
ImGui::Begin("My First Tool", &my_tool_active, ImGuiWindowFlags_MenuBar);
if (ImGui::BeginMenuBar())
{
if (ImGui::BeginMenu("File"))
{
if (ImGui::MenuItem("Open..", "Ctrl+O")) { /* Do stuff */ }
if (ImGui::MenuItem("Save", "Ctrl+S")) { /* Do stuff */ }
if (ImGui::MenuItem("Close", "Ctrl+W")) { my_tool_active = false; }
ImGui::EndMenu();
}
ImGui::EndMenuBar();
}
// Edit a color (stored as ~4 floats)
ImGui::ColorEdit4("Color", my_color);
// Plot some values
const float my_values[] = { 0.2f, 0.1f, 1.0f, 0.5f, 0.9f, 2.2f };
ImGui::PlotLines("Frame Times", my_values, IM_ARRAYSIZE(my_values));
// Display contents in a scrolling region
ImGui::TextColored(ImVec4(1,1,0,1), "Important Stuff");
ImGui::BeginChild("Scrolling");
for (int n = 0; n < 50; n++)
ImGui::Text("%04d: Some text", n);
ImGui::EndChild();
ImGui::End();
return 0;
}
Now this code doesn't compile due to my_tool_active and my_color, so I added these 2 lines to the code before the ImGui::Begin():
bool my_tool_active = true;
float my_color[4] = {0.5, 0.5, 0.5, 1};
So now when I compile and run, it gets to the ImGui::Begin() and then crashes at that stage. I have tried it in a much smaller example where it is just the ImGui::Begin() and ImGui::End() and placed print statements around it, and it showed that it never finished executing the Begin().

Answer 1

Imgui doesn't provide a graphics backend, neither it creates a window or a graphics API context. You have to provide it by yourself (using OpenGL/DirectX/Vulkan ecc...) or use a library that creates one for you (SDL/glfw ecc...).
Refer to the sample directory to a more complete sample.
This one is using sdl+openGl.
https://github.com/ocornut/imgui/blob/master/examples/example_sdl_opengl3/main.cpp