Declaring Local Object in C++

Question

One of the Question on C++ FAQ discusses correct way to declare local object within a function: http://www.parashift.com/c++-faq/fn-decl-vs-obj-instantiation.html

Given example from FAQ:

class Bar { 
public: 
  Bar();
};

class Foo {
public:
  Foo(Bar const& b);
  void blah();
};

void yourCode()
{
  Foo x(Bar());  // error     
}

In VS2012, error is Foo x(Bar (__cdecl *)(void))': prototyped function not called (was a variable definition intended?)

Could someone explain me why this this declaration gives an error ?(C++ FAQ explanation is too vague). Foo and Bar are both visible within body of yourCode(), and Foo x(Bar()); is a way I would declare an object of type Foo.

Some help: [most vexing parse](http://en.wikipedia.org/wiki/Most_vexing_parse) — zneak, Aug 23 '13 at 01:27
Not providing this as an answer as I'm sure its a dupe, As mentioned its called "most vexing parse" ... Fix is either add an extra set of brackets `Foo x((Bar()));` or extract the `Bar` instance as a variable `Bar bar; Foo x(bar);`. — Michael Anderson, Aug 23 '13 at 01:27
@C.R. Could you give this as answer ? I would gladly accept it. — newprint, Aug 23 '13 at 01:28
@newprint: Other people have more detailed answers. You could accept those. — Siyuan Ren, Aug 23 '13 at 01:33

score 6 · Accepted Answer · answered Aug 23 '13 at 01:30

As this C++'s the most vexing parse, you can do:

Foo x((Bar()));

or

Foo x = Bar();

The details are reviewed in the very parashift link you provided in your question.
Note though, the second example will break if the Foo copy constructor is made explicit.

score 0 · Answer 2 · answered Aug 23 '13 at 01:24

0

It looks like you've got a const consistency problem. The constructor for Foo wants a const Bar which Bar() isn't. Try:

const Bar b = Bar();
Foo x = Foo(b);

answered Aug 23 '13 at 01:24

Paul Evans

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@zneak, Then it takes an unnamed `Bar` as the parameter. The easiest fix is `Foo x{Bar{}};` imo, but it's C++11. – chris Aug 23 '13 at 01:39
Oh crap, you're right. – zneak Aug 23 '13 at 01:41
@zneak, Tricky C++ is tricky :p Anyway, I'll leave that since it hasn't been mentioned. – chris Aug 23 '13 at 01:41

Declaring Local Object in C++

2 Answers2