noexcept is a specifier declaring that a function will not throw exceptions (or will terminate if it does). A noexcept function enables compiler optimizations and is required for strong exception safety guarantees in moves and swaps. Misusing noexcept on code that can actually throw results in std::terminate.

Use noexcept on move constructors, move assignment, swaps, and other operations that standard containers rely on to be nothrow.

This example shows noexcept enabling optimizations and required for move operations.

// compile: g++ -o noexcept noexcept.cpp
// run: ./noexcept
// description: noexcept enables optimizations and satisfies container requirements
 
#include <iostream>
#include <vector>
#include <utility>
 
class SafeBuffer {
private:
    int* data;
    size_t size;
public:
    SafeBuffer(size_t n) : size(n), data(new int[n]) {}
 
    ~SafeBuffer() { delete[] data; }
 
    SafeBuffer(SafeBuffer&& other) noexcept
        : data(other.data), size(other.size) {
        other.data = nullptr;
    }
 
    SafeBuffer& operator=(SafeBuffer&& other) noexcept {
        delete[] data;
        data = other.data;
        size = other.size;
        other.data = nullptr;
        return *this;
    }
};
 
int main() {
    std::vector<SafeBuffer> v;
    v.push_back(SafeBuffer(100));  // move is noexcept, vector optimizes
 
    return 0;
}