problem: calling a template member function

[john.constantine]

Hi
I have this code:

[begin main.cpp]
template<typena me ClassType>
struct S
{
template<typena me FunctionType> void member() {};
};

template<typena me Type>
void g()
{
S<Type> s;
/*line 11*/ s.member<Type>( );
}

void h()
{
S<int> s;
s.member<int>() ;
}

int main(int, char**)
{
g<int>();
h();
return 0;
}
[end main.cpp]

I compile it with g++ (GCC) 3.4.2 (mingw-special) and get this compiler
error:
.../main.cpp: In function `void g()':
.../main.cpp:11: error: expected primary-expression before '>' token
.../main.cpp:11: error: expected primary-expression before ')' token

I do not understand what is wrong with the expression in Line 11 and
where the difference between the calls in g and h is.

Can anyone explain this?

TIA
Gabriel

[Frank Chang]

Gabriel, I took your code and compiled it with MSVC 7.1 , which
increases conformance with C++ standard. It compiled and ran OK. I know
MSVC7.1 and g++ 3.4.2 are different but don't both compilers try to
conform with C++ standard? Thank you

[Gabriel]

Frank Chang wrote:

Gabriel, I took your code and compiled it with MSVC 7.1 , which
increases conformance with C++ standard. It compiled and ran OK. I know
MSVC7.1 and g++ 3.4.2 are different but don't both compilers try to
conform with C++ standard? Thank you

Thank you, Frank

Yes, I think that they both try to conform to the standard. And I think
g++ 3.4 (or later) is very close to the standard. As far as I understand
the language, my code should be correct, but I am not sure if the g++
should translate it or if the MSVC makes a mistake by translating it.

If it's a problem with the g++, does anyone know a workaround?

[Gabriel]

Some additional information:

I just ran it under the IAR Embedded Workbench IDE with the MSP430 IAR
C/C++ Compiler, and it tells me

Error[Pe254]: type name is not allowed H:\Projects\Tes t (IAR Embedded
Workbench IDE)\main.cpp 11
Error[Pe029]: expected an expression H:\Projects\Tes t (IAR Embedded
Workbench IDE)\main.cpp 11

Gabriel

[annamalai.gurusami]

Gabriel wrote:

If it's a problem with the g++, does anyone know a workaround?

FWIW, The code that you posted doesn't compile with g++ 3.3.4 as well.
Anyway, as a work around you can add a dummy parameter to the
templated member function.

template<typena me ClassType>
struct S
{
template<typena me FunctionType> void member(Function Type* t =0) {};
};

template<typena me Type>
void g()
{
S<Type> s;
s.member( static_cast<Typ e*>(0) );
}

Rgds,
anna

[Victor Bazarov]

john.constantin e wrote:

Hi
I have this code:

[begin main.cpp]
template<typena me ClassType>
struct S
{
template<typena me FunctionType> void member() {};
Drop the trailing semicolon: while it is not a severe violation,
it is entirely superfluous and a bad habit.
};

template<typena me Type>
void g()
{
S<Type> s;
/*line 11*/ s.member<Type>( );
Needs to be
s.template member<Type>();

to be standard C++. MS compiler hasn't got there yet.
}

void h()
{
S<int> s;
s.member<int>() ;
}

int main(int, char**)
{
g<int>();
h();
return 0;
}
[end main.cpp]

I compile it with g++ (GCC) 3.4.2 (mingw-special) and get this compiler
error:
../main.cpp: In function `void g()':
../main.cpp:11: error: expected primary-expression before '>' token
../main.cpp:11: error: expected primary-expression before ')' token

I do not understand what is wrong with the expression in Line 11 and
where the difference between the calls in g and h is.

Can anyone explain this?

A template member of a template needs to be specified as such to help
the compiler resolve the name. I don't remember the exact paragraph
of the Standard, but you could search the archives on Google, it has
come up more than once in this newsgroup.

V

[Gabriel]

an************* ***@gmail.com wrote:

Gabriel wrote:

If it's a problem with the g++, does anyone know a workaround?

FWIW, The code that you posted doesn't compile with g++ 3.3.4 as well.
Anyway, as a work around you can add a dummy parameter to the
templated member function.

template<typena me ClassType>
struct S
{
template<typena me FunctionType> void member(Function Type* t =0) {};
};

template<typena me Type>
void g()
{
S<Type> s;
s.member( static_cast<Typ e*>(0) );
}

Rgds,
anna

That's a nifty solution! I think that will help me out for now...
Thanx anna!

Gabriel

[Gabriel]

Victor Bazarov wrote:

john.constantin e wrote:

Hi
I have this code:

[begin main.cpp]
template<typena me ClassType>
struct S
{
template<typena me FunctionType> void member() {};

Drop the trailing semicolon: while it is not a severe violation,
it is entirely superfluous and a bad habit.

};

template<typena me Type>
void g()
{
S<Type> s;
/*line 11*/ s.member<Type>( );

Needs to be
s.template member<Type>();

to be standard C++. MS compiler hasn't got there yet.

}

void h()
{
S<int> s;
s.member<int>() ;
}

int main(int, char**)
{
g<int>();
h();
return 0;
}
[end main.cpp]

I compile it with g++ (GCC) 3.4.2 (mingw-special) and get this
compiler error:
../main.cpp: In function `void g()':
../main.cpp:11: error: expected primary-expression before '>' token
../main.cpp:11: error: expected primary-expression before ')' token

I do not understand what is wrong with the expression in Line 11 and
where the difference between the calls in g and h is.

Can anyone explain this?

A template member of a template needs to be specified as such to help
the compiler resolve the name. I don't remember the exact paragraph
of the Standard, but you could search the archives on Google, it has
come up more than once in this newsgroup.

V

Thank you, Victor.
I have never seen this before. Even in the Stroustrup I could not find it.

What I still not understand is why the call in h is valid and the call
in (the template function) g is not valid.

Gabriel

[Victor Bazarov]

Gabriel wrote:

Victor Bazarov wrote:

john.constantin e wrote:

Hi
I have this code:

[begin main.cpp]
template<typena me ClassType>
struct S
{
template<typena me FunctionType> void member() {};

Drop the trailing semicolon: while it is not a severe violation,
it is entirely superfluous and a bad habit.

};

template<typena me Type>
void g()
{
S<Type> s;
/*line 11*/ s.member<Type>( );

Needs to be
s.template member<Type>();

to be standard C++. MS compiler hasn't got there yet.

}

void h()
{
S<int> s;
s.member<int>() ;
}

int main(int, char**)
{
g<int>();
h();
return 0;
}
[end main.cpp]

I compile it with g++ (GCC) 3.4.2 (mingw-special) and get this
compiler error:
../main.cpp: In function `void g()':
../main.cpp:11: error: expected primary-expression before '>' token
../main.cpp:11: error: expected primary-expression before ')' token

I do not understand what is wrong with the expression in Line 11 and
where the difference between the calls in g and h is.

Can anyone explain this?

A template member of a template needs to be specified as such to help
the compiler resolve the name. I don't remember the exact paragraph
of the Standard, but you could search the archives on Google, it has
come up more than once in this newsgroup.

V

Thank you, Victor.
I have never seen this before. Even in the Stroustrup I could not find it.

What I still not understand is why the call in h is valid and the call
in (the template function) g is not valid.

'h' is not a template itself. 'g' is a template. The names are resolved
differently inside those scopes. Get a copy of "C++ Templates" by David
Vandevoorde and Nicolai Josuttis. It's an extremely helpful book. It
doesn't just tell you how, it explains why certain things are done the way
they are done.

V

[annamalai.gurusami]

Victor Bazarov wrote:

Needs to be
s.template member<Type>();

to be standard C++. MS compiler hasn't got there yet.

I haven't yet written (or maintained) template heavy C++ code.
So, this is new for me (obvious, if you had a look at my
previous post, which the OP was kind enough to call nifty.)

My question is if the original code was incorrect, and MS
compiler compiled it successfully, what does it mean? Will
the MS compiler generate wrong object code for correct
(standard compliant) C++ code, in some very rare cases?
(Probably template heavy stuff.)

Any thoughts on that?

Rgds,
anna