Talk:cpp/language/scope
From cppreference.com
[edit] Scope and object Lifetime
Below is a proposed code example demonstrating the effect of scope on object lifetime. Modification of current code in the destructor article.
This isn't a comprehensive list, but it does demonstrate the unnoticed side effects of plain old scope brackets.
Run this code
#include <iostream> struct A { int i; A ( int i ) : i ( i ) { std::cout << "Calling Constructor:\t a" << i << '\n'; } ~A() { std::cout << "Calling Destructor:\t a" << i << '\n'; } }; A a0(0); //In global scope. Construted first, destroyed last void ScopeTest1() { A a1(1); //a1 in function scope. Destroyed on exiting function scope A* p; //Pointer only. No object contructed yet. { // nested scope A a2(2); //a2 in nested scope. Destroyed at end of current scope {//further nested scope A a3(3); //a3 Destroyed at end of this scope } //a3 out of scope {//further nested scope A a4(4); //a4 Destroyed at end of this scope A a5(5); //a5 Destroyed at end of this scope } //a4 out of scope p = new A(6); //a5 created on heap. Infinite lifetime until destroyed by call to delete. } // a2 out of scope delete p; // calls the destructor of a5 } //a1 out of scope. //p out of scope (But a5) void f(){ std::cout << "Calling f()" << std::endl; } int main(){ ScopeTest1(); std::cout << std::endl; f(),A(7),f(),f(); //Statement scope. Unnamed instance destroyed at end of statement A a8(8); { A& a9 = a8; //References and pointers fall out of scope A* a10 = &a8; //but underlying object not deleted } return 0; }
Output:
Calling Constructor: a0 Calling Constructor: a1 Calling Constructor: a2 Calling Constructor: a3 Calling Destructor: a3 Calling Constructor: a4 Calling Constructor: a5 Calling Destructor: a5 Calling Destructor: a4 Calling Constructor: a6 Calling Destructor: a2 Calling Destructor: a6 Calling Destructor: a1 Calling f() Calling Constructor: a7 Calling f() Calling f() Calling Destructor: a7 Calling Constructor: a8 Calling Destructor: a8 Calling Destructor: a0
[edit] Link to undefined term
class-head links to Classes but the term doesn't occur there.
