Beware of auto[&] (c++)

auto deduces its types from initializing expressions, and occasionally, these expressions have unexpected types, which are not what you want. On the other hand, auto has many benefits. - Don’t use C++ auto?

int& f();

auto a = f();       // BEWARE! a => is int
auto& a = f();	 	// a => is int&

int x = 0;
int& r = x;
const int& cr = x;

const auto& v = x;   // v’s type is “const int&”; auto is “int"
const auto& cv = cr;   // cv’s type is “const int&”; auto is “int"
auto* w = &r;   // w’s type is “int*”; auto is “int"
auto* cw = &cr;   // cw’s type is “const int*”; auto is “const int”

std::vector<int> vec({1, 2, 3, 4, 5});

auto& first = vec[0];   // first's type is "int&”; auto is “int”

Written on February 1, 2018, Last update on September 23, 2020

c++