Comparison of float parsing with istream & other methods in native & emscriptens compilers.

main.cpp

#include <iostream>
#include <sstream>
#include <cstdlib>
#include <locale>
using namespace std;

int main() {
	string s = "23.4f";
	stringstream stream(s);
	float f;
	char c;
	cout << "Flags = " << stream.flags() << endl;
	cout << "Using locale " << stream.getloc().name() << endl;
	stream >> f;
	stream.get(c);
	cout << endl << "istream:" << endl;
	cout << "Float = " << f << endl << "Character = " << c << endl;

	stringstream stream2(s);
	auto loc = stream2.getloc();
	auto& ng = use_facet<num_get<char, istreambuf_iterator<char>>>(loc);
	istreambuf_iterator<char> beg{stream2}, end;
	ios::iostate state = {};
	f = 0;
	ng.get(beg, end, stream2, state, f);
	cout << endl << "num_get:" << endl;
	cout << "Float = " << f << endl << "state = " << state << endl;
	
	char* endptr = NULL;
	f = strtof(s.c_str(), &endptr);
	cout << endl << "strtof:" << endl;
	cout << "Float = " << f << endl;
	if (endptr == NULL)
		cout << "Endptr is NULL" << endl;
	else
		cout << "Endptr is shifted by " << endptr - s.c_str() << endl;

	cout << endl << "sscanf:" << endl;
	f = 0;
	int chars_consumed = 0;
	sscanf(s.c_str(), "%g%n", &f, &chars_consumed);
	cout << "Float = " << f << endl << "# of consumed characters = " << chars_consumed << endl;

	return 0;
}

Makefile

run: main main.js
	@echo "=== Native ==="
	./main
	@echo
	@echo "=== Emscripten ==="
	node ./main.js
main: main.cpp
	g++ -std=c++11 main.cpp -o main
main.js: main.cpp
	em++ -std=c++11 main.cpp -o main.js
.PHONY: run