main_loop_with_lambda.cpp

#include <emscripten.h>
#include <functional>
#include <numeric>
#include <cassert>
#include <iostream>

std::function<void()> mainLoop;

void runMainLoop() 
{
	mainLoop();
}

void userMain() 
{
  	// allocate someData onto the stack
	int someData[100]; // [ 0, 1, , ... , 99 ]

	std::iota(std::begin(someData), std::end(someData), 0);

	// Check values in someData
	for (int i = 0; i < 100; i++)
	{
		std::cout << someData[i] << std::endl;
		assert(someData[i] == i);
	}

	mainLoop = [&]() 
	{
    	// someData is captured by lambda, so we can use it here.
    
		// Some works here on the stack
		{
			int anyData[100]; // [ 99, 98, ... , 0 ]
			std::iota(std::rbegin(anyData), std::rend(anyData), 0);
		}
		
		// Any operations with the stack should not affect someData in this lambda
    	// let's check values in someData
		for (int i = 0; i < 100; i++)
		{
			std::cout << someData[i] << std::endl;
			assert(someData[i] == i);
		}

		::emscripten_cancel_main_loop();
	};

	::emscripten_set_main_loop(&runMainLoop, 0, true);
}

int main() 
{
	try
	{
		userMain();
	}
	catch (const std::exception& e)
	{
		std::cout << e.what() << std::endl;
	}

	return 0;
}