constructor syntax in c++
struct S {
int n;
S(int); // constructor declaration
S() : n(7) {} // constructor definition.
// ": n(7)" is the initializer list
// ": n(7) {}" is the function body
};
S::S(int x) : n{x} {} // constructor definition. ": n{x}" is the initializer list
int main()
{
S s; // calls S::S()
S s2(10); // calls S::S(int)
}