Inject a user header file into a library

erincatto · December 26, 2023, 6:50pm

Is there a good pattern for a user to optionally inject a user header file into my library? This would setup some defines that override default defines and doesn’t require putting these defines into every compilation call. Of course this would only work in source builds and binary builds would not be able to use this feature.

An example is the imgui file imconfig.h. imgui doesn’t use CMake though.

github.com

ocornut/imgui/blob/master/imconfig.h

//-----------------------------------------------------------------------------
// DEAR IMGUI COMPILE-TIME OPTIONS
// Runtime options (clipboard callbacks, enabling various features, etc.) can generally be set via the ImGuiIO structure.
// You can use ImGui::SetAllocatorFunctions() before calling ImGui::CreateContext() to rewire memory allocation functions.
//-----------------------------------------------------------------------------
// A) You may edit imconfig.h (and not overwrite it when updating Dear ImGui, or maintain a patch/rebased branch with your modifications to it)
// B) or '#define IMGUI_USER_CONFIG "my_imgui_config.h"' in your project and then add directives in your own file without touching this template.
//-----------------------------------------------------------------------------
// You need to make sure that configuration settings are defined consistently _everywhere_ Dear ImGui is used, which include the imgui*.cpp
// files but also _any_ of your code that uses Dear ImGui. This is because some compile-time options have an affect on data structures.
// Defining those options in imconfig.h will ensure every compilation unit gets to see the same data structure layouts.
// Call IMGUI_CHECKVERSION() from your .cpp file to verify that the data structures your files are using are matching the ones imgui.cpp is using.
//-----------------------------------------------------------------------------

#pragma once

//---- Define assertion handler. Defaults to calling assert().
// If your macro uses multiple statements, make sure is enclosed in a 'do { .. } while (0)' block so it can be used as a single statement.
//#define IM_ASSERT(_EXPR)  MyAssert(_EXPR)
//#define IM_ASSERT(_EXPR)  ((void)(_EXPR))     // Disable asserts

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I’m currently using configure_file() and wondering if this is the best approach.

ben.boeckel · December 26, 2023, 7:04pm

configure_file helps to make the header, but there’s no mechanism to force anything using your library to include it beyond making it a transitive include of your primary headers.