So, in this example program, I demonstrate the move operators. Their purpose is to do a shallow copy of an object: copy all pointers rather than pointer contents. The ephemeral source object is now considered to have an invalid state and is probably going out of scope soon.
In this program, I create an object, A, and it allocates dynamic memory. I then move construct an object, B, which now has all of A’s data, no deep copies involved. The addresses of each variable, demonstrating they were not reallocated, are printed.
class A {
public:
std::vector<int> v;
std::string str;
std::mutex m;
A() {
v.resize(100);
str.resize(100);
}
A( A&& a) noexcept {
v = std::move(a.v);
str = std::move(a.str);
}
void printAddresses() {
std::cout << std::hex;
auto print = [&](const auto& c, auto pointer) {
std::cout << c << ": 0x" << std::size_t(pointer)
<< std::endl;
};
print("v", v.data());
print("str", str.data());
print("m", &m);
}
};
int main() {
A a;
std::cout << "before move\n";
a.printAddresses();
A b(std::move(a));
std::cout << "after move\n";
std::cout << "a:";
a.printAddresses();
std::cout << "\nb:";
b.printAddresses();
return 0;
}
Spot C++ 