Instantiating objects without calling the constructor in C++ -

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• c++ default constructor not being called 2 answers

i'm new @ c++ , i'm learning constructors. have class dog constructor:

class dog{     dog(){         std::cout << "constructor called!     } }; 

i know in c++ there different ways(if i'm not mistaken) can create object, instance:

1- dog dog; 2- dog dog = dog(); 3- dog *dog = new dog; 4- dog *dog = new dog(); 5- dog dog(); 

but here thing: statements 1 4 call constructor, statement number 5 doesn't , can figure out why.

do have idea why fifth statement doesn't call class constructor? thanks.

5 example of c++'s most vexing parse.

dog dog(); 

this declares function named dog accepts no parameters , returns dog. avoid most vexing parse (and if using c++11), can do:

dog dog{}; 

and semantically (at least until c++17), dog dog = dog(); first create temporary object (dog()), , move construct (or copy construct, if dog class has no move constructor) named object (dog) it. although compilers might optimize move away, statement have different semantics rest.

if remember correctly, since c++17, p0135r0 change semantics of dog dog = dog(); has same meaning dog dog;.

edit: pointed out @lightnessracesinorbit in comments, dog dog(); vexing, not quite vexing parse. dog dog(dog()); true vexing parse. dog dog(); a, well, plain declaration, guess.