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C++17 in Detail: A Deep Dive

For_Each and Reduce Algorithms

Learn how to use the for_each and std::reduce algorithms in C++17, including their parallel capabilities, to efficiently process data. Understand the differences between sequential and parallel operations, and the impact of commutative and associative properties on results.

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for_each Algorithm

In the serial version of for_each, the version that was available before C++17 you get a unary function as a return value from the algorithm.

Returning such an object is not possible in a parallel version, as the order of invocations is indeterminate.

Here’s a basic example:

C++
void ForEachTest() {
	std::vector<int> v(100);
	std::iota(v.begin(), v.end(), 0);
	std::for_each(std::execution::par, v.begin(), v.end(),
		[](int& i) { i += 10; });
	std::for_each_n(std::execution::par, v.begin(), v.size() / 2,
		[](int& i) { i += 10; });
}
int main() {
	ForEachTest();
	return 0;
}

The first for_each algorithm will update all of the elements of a vector, while the second execution will work only on the first half of the container.

Understanding Reduce Algorithms

Another core algorithm that is ...