inlining and copy constructors

**ChaosEngine** · 10-13-2005

if I have a templated inline function that takes an object by value
i.e.

Code:

template <typename T>
void DoSomething(T someT)
{
    // assume << is defined!!
    cout << someT;
}

if this function is called and inlined will T's copy ctor still get called?
i.e.

Code:

ExpseniveToCopy etc;
DoSomething(etc);

//becomes either
ExpseniveToCopy etc;
cout <<etc;

// or

ExpseniveToCopy etc;
ExpseniveToCopy someT(etc);
cout << someT;

I presume it's the latter, but can't find anything definite (and I can't use a reference, as DoSomething sometimes accepts a reference and reference to a reference is illegal)

**Dante Shamest** · 10-13-2005

(and I can't use a reference, as DoSomething sometimes accepts a reference and reference to a reference is illegal)

Hmm, is that so? I thought it should work. Do you mean something like this?

Code:

#include <cstdlib>
#include <iostream>
using namespace std;

template <typename T>
void DoSomething(T& someT){
  cout << someT;
}

int main(int argc, char *argv[])
{
  int a = 2;
  int& b = a ;
  DoSomething( b );
  cin.get();
  return 0 ;
}

**ChaosEngine** · 10-13-2005

allow me to rephrase. ref to ref may or may not be illegal but VS.net2k3 spits out the following error

error C2529 : reference to reference is illegal

**Thantos** · 10-13-2005

Yes a reference to a reference would be illegal and it makes no sense. However you can initalize a reference with an object that is a reference.

Code:

int a = 5;
int& b = a;
int&& c = b; // not legal

Code:

int a = 5;
int& b = a;
int& c = b; // legal

**ChaosEngine** · 10-13-2005

Originally Posted by Thantos

Yes a reference to a reference would be illegal and it makes no sense. However you can initalize a reference with an object that is a reference.

the problem is that sometimes the type can't be deduced so you have to specify it (this happens specifically with mem_fun and bind2nd)

check out this thread on gamedev.net for more info.

**Thantos** · 10-13-2005

Ok I'm still not seeing your problem. Can you show me some actual code that invokes this behavior?

**Daved** · 10-14-2005

You might consider asking this question on comp.lang.c++(.moderated) or the CodeGuru forums. They have a lot more active advanced users than there are here.

**pianorain** · 10-14-2005

Originally Posted by ChaosEngine

if this function is called and inlined will T's copy ctor still get called?

It's simple enough to try yourself.

Code:

#include <iostream>

class A
{
public:
  A() {}
  A(const A& obj) {std::cout
    << "Copy Constructor" << std::endl;}
};

template <typename T>
inline void DoSomething(T someT) {}

int main()
{
  A a;
  DoSomething( a );
  return 0 ;
}

Originally Posted by ChaosEngine

allow me to rephrase. ref to ref may or may not be illegal but VS.net2k3 spits out the following error

error C2529 : reference to reference is illegal

Good, you gave us half of it. Now, let's see the code that generates this error.

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