C / C++ / MFC

4-Sep-04 16:18

I can't compile the following code:

class Foo
{
public:
  template< class T > void F() { T t; }
};

void main()
{
  Foo tmp;
  tmp.F < bool >();
}

The compile raises the error:

<br />
_samples.cpp(10) : error C2275: 'bool' : illegal use of this type as an expression<br />
_samples.cpp(0) : see declaration of 'bool'<br />

It raises the same error if I replace the bool type by a class.
It works if F is not declared as a member function.

It also works fine like this:

class Foo
{
public:
  template<class T> void F(T bool) { T t; }
};

void main()
{
  Foo tmp;
  tmp.F(true);
}

How to do the call to have this working without having the type in param???

PJ Arends4-Sep-04 17:15

PJ Arends

4-Sep-04 17:15

You have to declare the class as a template class.

template <class T> class foo
{
    void F (T var) { cout << var; } // function 'F' takes a parameter of type T
};
 
void main()
{
    bool b = true;
    foo<bool> tmp;  // an instance of 'class foo' that takes a 'bool'
    tmp.F(b);
}

"You're obviously a superstar." - Christian Graus about me - 12 Feb '03

"Obviously ??? You're definitely a superstar!!!" mYkel - 21 Jun '04

Within you lies the power for good - Use it!

Kandjar4-Sep-04 18:06

4-Sep-04 18:06

No, it's not the same purpose. Smile | :)

I really need the template for the member function, not for the class.

It's only for one function, not for the whole class Smile | :)

PJ Arends4-Sep-04 23:15

PJ Arends

4-Sep-04 23:15

class foo
{
    template <class T> void F (T var) { cout << var; }
};
 
void main()
{
    bool B = true;
    foo Foo;
    Foo.F(B);
}

"You're obviously a superstar." - Christian Graus about me - 12 Feb '03

"Obviously ??? You're definitely a superstar!!!" mYkel - 21 Jun '04

Within you lies the power for good - Use it!

Kandjar5-Sep-04 12:26

5-Sep-04 12:26

Yep, but it's not what I really wanna do Smile | :)

And in this case I prefer doing:
template < class T > void F (T *var) { ... }
and:
Foo.F((bool*)0);

Doing this way, the T object is not construct.
Nonetheless, it's a bit dodgie...

Antti Keskinen5-Sep-04 1:22

Antti Keskinen

5-Sep-04 1:22

This is kinda difficult.. I used the following code piece:

class Foo
{
public:
   template<typename T> void F() { T var; }
};<DIV>

void main()
{
   Foo tmp;
   tmp.F<bool>();
}

This piece of code compiles properly, but issues a warning about an unreferenced local variable var which is what it should do as well.

Also, the first code piece you posted also compiles properly, but issues the same warning. I am using Visual Studio .NET 2003, so perhaps it's a compiler bug ?

-Antti Keskinen

----------------------------------------------
The definition of impossible is strictly dependant
on what we think is possible.

Kandjar5-Sep-04 11:59

5-Sep-04 11:59

I guess it's a compiler issue.. I'm using VC6 sp5 Frown | :(

I send this code to one on my friend which got exactly the same problem.

Worst: if you try to change the member function into a static member function, the compiler crashes.

Michael Dunn5-Sep-04 6:11

Michael Dunn

5-Sep-04 6:11

Kandjar wrote:
template< class T > void F() { T t; }

That is a known problem in VC 6, that arises when the template parameter isn't present in the prototype. The common workaround is:

template< class T > void F(T* unused=NULL) { ... }

--Mike--
Personal stuff:: Ericahist | Homepage
Shareware stuff:: 1ClickPicGrabber | RightClick-Encrypt
CP stuff:: CP SearchBar v2.0.2 | C++ Forum FAQ
----
Martin Kolberg, head of the local animal committee in Telemark, warns people to beware of drunken moose.
If my rhyme was a drug, I'd sell it by the gram.

Kandjar5-Sep-04 12:03

5-Sep-04 12:03

I tried, but I'm still unable to do:
tmp.F< bool >();

Am I obliged to do
tmp.F((bool*)0);
to be able to use it?

hex digit format

S.W.4-Sep-04 11:32

S.W.

4-Sep-04 11:32

I would like my output to be 4 hex digits.
0000 0001 0002 ... 000a 000b ... 0015

I am using the following loop to do this:

<br />
   for (int i = 0; i <= 21; i++)<br />
   {<br />
	   cout << setw(5) << hex << i << endl;<br />
   } // END for<br />

It currently displays as
0 1 ... a b ... 15

Any help would be appreciated.

S.W.

Archer2824-Sep-04 15:22

Archer282

4-Sep-04 15:22

printf( "%04x", 255 );

output will be
00FF

so what you want is probably

for( int i = 0; i <= 21; i++ )
{
printf( "%04x\n", i );
}

S.W.4-Sep-04 15:41

S.W.

4-Sep-04 15:41

Thanks Archer,

Would you mind breaking the statement down for me or maybe you know of a link that would explain it to me. I appreciate your time.

David Crow4-Sep-04 16:37

David Crow

4-Sep-04 16:37

Keep in mind that cout and printf() are not the same thing. The former is C++ while the later is C.

For a purely C++ solution, you simply need:

cout.fill('0');
cout << setw(5) << hex << i << endl;

"When I was born I was so surprised that I didn't talk for a year and a half." - Gracie Allen