Difference between declaring a C++ object with/without braces

Question

Possible Duplicate:
constructor invocation mechanism

It took me long to figure this problem. So I was curious to know the difference between them. Below is the code snippet:

struct Test
{
  Test () { cout<<" Test()\n"; }
 ~Test () { cout<<"~Test()\n"; }
};
int main()
{
  Test obj(); // Remove braces of 'obj' & constructor/destructor are printed
}

Wanted to know that, why such behavior ? Is there any fundamental difference between declaring an object with/without empty braces (here we talk only about the cases of default constructor). Code is compiled one of the latest versions of Ubuntu/g++. Sorry if, it's a repeat question.

This is a dupe! Check out [this thread](http://stackoverflow.com/questions/4283576/constructor-invocation-mechanism/) — Prasoon Saurav, Mar 23 '11 at 04:26
Just as an aside, *braces* are `{}`, but *parentheses* are `()`. I couldn't figure out what you meant until I realised that you were talking about the `()`. — Greg Hewgill, Mar 23 '11 at 04:35

score 2 · Accepted Answer · answered Mar 23 '11 at 04:24

2

Test obj();

declares a function named obj that takes no parameters and returns an object of type Test. It does not create an object obj of type Test with the default constructor.

answered Mar 23 '11 at 04:24

Jesse Beder

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Oh.. thanks. I forgot that fundamental. I kept empty braces to emphasize that, this is indeed a default constructor to the viewer. But messed up with another (forward declaration) feature. :) I usually do this, with operator 'new Struct()', but missed that, we can't do it with stack objects. – iammilind Mar 23 '11 at 04:29
@prasoon, yes I see. Will try for it. – iammilind Mar 23 '11 at 04:34

score 0 · Answer 2 · answered Mar 23 '11 at 04:25

Test obj(); means that declaring a function named obj() whose return type is Test. Statement is not actually instantiating class Test. For the class to be instantiated -

Test obj ; // obj is instantiated meaning it's constructor is called and 
           // destructor is called when gone out of scope.

Difference between declaring a C++ object with/without braces

2 Answers2