hot_patch

Introduction

The hot_patch module (hot_patch.c + hot_patch.h) is a small and straight forward implementation of a very useful concept: the ability to edit certain constants in your code, and to make your (running) application immediately take them in account without having to recompile said program.

How it works

• Pass the values of the constants you want to be able to have live access to to the _HP macro
• Compile your application in debug mode with the hot_patch module (the module considers the application is in debug mode if the DEBUG macro is defined)
• Run your application in a separate terminal/window
• Edit the content of the _HP macros in your source code, save the file
• Profit !

Example

Compile the following code with the hot_patch module (don't forget to define the DEBUG macro, with the -D option for example).

int main() {
	int editable = _HP(int, 1);
	while (editable) {
		fprintf(stdout, "Editable: %d\n", editable);
		sleep(3);
	}

	return 0;
}

Run the resulting binary in a separate window , and edit the '1' in the _HP macro by.. something else, and watch your app display "Editable: SOMETHING_ELSE".

Note that the first field of the macro is mandatory, as it represents the type of the editable variable. Consequently, modifying it at runtime will result in an undefined behavior.

Fields of use

Although this module is kind of a PoC (Proof of Concept), I find it really handy to have when I have to code applications that use "constants" I don't really know the value they should take when I'm developing the application. E.g: for debugging purpose, I like to change the gravity of my game engines at runtime: it spares me the parsing of a configuration file/the recompilation of the whole game. It could also be used to change the maximum number of FPS your game runs at, or the maximum number of entities that are to be updated every second.