struct->struct->class in C++ no constructor

struct->struct->class in C++ no constructor

[Wesley Smith]

Hi,
I've encountered a problem in GCC 4.2.3 that didn't exist in GCC
4.0.x.  Let's say I have:

template<class T>
Tube{
public:
    Tube();
    ~Tube();
};

struct Graph {
   Tube<Ugen> t;
}

struct Clock {
   Graph g;
}

At issue is that Tube<T>'s constructor isn't getting called when Clock
is allocated on the stack.  Is this compliant with the C++ standard?
I thought all classes had their constructors called when instantiated
as an object even as members of structs.  Any ideas?

thanks,
wes

Re: struct->struct->class in C++ no constructor

[Chris Jefferson]

2008/7/21 Wesley Smith <wesley.hoke@gmail.com>:
> Hi,
> I've encountered a problem in GCC 4.2.3 that didn't exist in GCC
> 4.0.x.  Let's say I have:
>
> template<class T>
> Tube{
> public:
>    Tube();
>    ~Tube();
> };
>
> struct Graph {
>   Tube<Ugen> t;
> }
>
> struct Clock {
>   Graph g;
> }
>
> At issue is that Tube<T>'s constructor isn't getting called when Clock
> is allocated on the stack.  Is this compliant with the C++ standard?
> I thought all classes had their constructors called when instantiated
> as an object even as members of structs.  Any ideas?

Can you give a complete program which shows your problem?

Chris

Re: struct->struct->class in C++ no constructor

[John Fine]

Can you provide a complete example?

As you described it, the constructor should be called.  But you haven't 
given enough information for anyone to duplicate the situation in which 
the constructor isn't called.

Was the definition of the constructor provided in the same compilation 
or was it external?  If provided, how do you know it wasn't called 
(possibly inlined and optimized to the point that you wouldn't know)?

Wesley Smith wrote:
>
> At issue is that Tube<T>'s constructor isn't getting called when Clock
> is allocated on the stack.  Is this compliant with the C++ standard?
> I thought all classes had their constructors called when instantiated
> as an object even as members of structs.  Any ideas?
>
>
>   

Re: struct->struct->class in C++ no constructor

[Wesley Smith]

Hi,
I had a breakpoint in the constructor, so I know it wasn't called.
Also had some print statements in there.  It's a non trivial function,
so it shouldn't be optimized out and I'm also building debug.  I'll
try and extract it from the project and post a concrete example.

thanks,
wes

On Mon, Jul 21, 2008 at 2:18 PM, John Fine <johnsfine@verizon.net> wrote:
> Can you provide a complete example?
>
> As you described it, the constructor should be called.  But you haven't
> given enough information for anyone to duplicate the situation in which the
> constructor isn't called.
>
> Was the definition of the constructor provided in the same compilation or
> was it external?  If provided, how do you know it wasn't called (possibly
> inlined and optimized to the point that you wouldn't know)?
>
> Wesley Smith wrote:
>>
>> At issue is that Tube<T>'s constructor isn't getting called when Clock
>> is allocated on the stack.  Is this compliant with the C++ standard?
>> I thought all classes had their constructors called when instantiated
>> as an object even as members of structs.  Any ideas?
>>
>>
>>
>
>

Re: struct->struct->class in C++ no constructor

[Alexandre Oliva]

On Jul 21, 2008, "Wesley Smith" <wesley.hoke@gmail.com> wrote:

> At issue is that Tube<T>'s constructor isn't getting called when Clock
> is allocated on the stack.

Two thoughts:

- copy constructor being called instead

- syntax that declares a function returning a Clock, rather than an
object of type Clock

Without the definition, it's hard to give any definitive answer.

-- 
Alexandre Oliva         http://www.lsd.ic.unicamp.br/~oliva/
Free Software Evangelist  oliva@{lsd.ic.unicamp.br, gnu.org}
FSFLA Board Member       ¡Sé Libre! => http://www.fsfla.org/
Red Hat Compiler Engineer   aoliva@{redhat.com, gcc.gnu.org}

Re: struct->struct->class in C++ no constructor

[Eljay Love-Jensen]

Hi Wes,

Worked on my machine.  [See code below.]

Can you provide a compile-able example which illustrates the problem?

The example you provided was too abbreviated, and did not compile.

Thanks,
--Eljay

- - - -

#include <iostream>

template <typename T>
class Tube
{
public:
  Tube();
  ~Tube();
};

template <typename T>
Tube<T>::Tube()
{
  std::cerr << "Tube ctor\n";
}

template <typename T>
Tube<T>::~Tube()
{
  std::cerr << "Tube dtor\n";
}

typedef int Ugen;

struct Graph
{
  Tube<Ugen> t;
};

struct Clock
{
  Graph g;
};

void TestOnStack()
{
  Clock clock;
}

int main()
{
  TestOnStack();
}