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From: Kris Prad on 4 Dec 2009 02:08
I have no particular reason to do this, but consider the instantiation
of this:

template<int N> struct A
{
A()
{
cout << "Value of N is: " << N << endl;
}
};

A<__LINE__> a; // does not compile in VS2008
// But compiles in Comeau online.

// This one compiles in both
static const int LINE = __LINE__;
A<LINE> a;

Preprocessor is not part of the standard, so both are correct? VS2008,
however, appears to be inconsistent.





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From: Chris Morley on 5 Dec 2009 07:06
> I have no particular reason to do this, but consider the instantiation
> of this:
>
> template<int N> struct A
> {
> A()
> {
> cout << "Value of N is: " << N << endl;
> }
> };
>
> A<__LINE__> a; // does not compile in VS2008
> // But compiles in Comeau online.
>
> // This one compiles in both
> static const int LINE = __LINE__;
> A<LINE> a;
>
> Preprocessor is not part of the standard, so both are correct? VS2008,
> however, appears to be inconsistent.

You need some preprocessor trickery. Quick adaption of the macros I use to
produce line numbered temp variables (useful within other macros so you
don't get variable name clashes) appends zero onto the front of line & feeds
that to the foo<>.

This compiles fine in VS2008.

#include <stdio.h>

#define _LINENAME_CAT( name, line ) name##line
#define _LINENAME( name, line ) _LINENAME_CAT( name, line )
//#define LINED( name ) _LINENAME( name, __LINE__ )
#define LINED _LINENAME( 0, __LINE__ )

template< int N > struct foo {
void print() {printf("My number is: %d\n",N);}
};

int main(int argc, char**argv) {
foo< LINED > a;
foo< LINED > b;

a.print();
b.print();
}


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From: Kenneth 'Bessarion' Boyd on 6 Dec 2009 03:21
On Dec 4, 1:08 pm, Kris Prad <krisp...(a)yahoo.co.uk> wrote:

> Preprocessor is not part of the standard, so both [MSVC and Comeau] are
correct?

The preprocessor gets an entire chapter of both the C++ and C
standards, as well as explicit mention in the stages of compilation.
However, in many aspects Microsoft C++ and C compiliers appear to have
feature-frozen or architecture-frozen between 1990 and 1999.

> VS2008, however, appears to be inconsistent.

VS2008 is failing to implement C++98 and higher. [section lex.phases;
C++98 2.1/C++0X n3000 2.2 are materially identical]. VS2008 evidently
is trying to interpret templates (part of stage 7) before logically
completing handing preprocessing (stage 4).

I assume VS2008 is implementing some pre-standard draft of C++ in
regard to when templates are parsed, but can't verify which one
quickly [do not have the relevant drafts downloaded].


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