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mysterious snippet

 
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khaeming@web.de
Guest
PostPosted: Tue Oct 18, 2005 10:23 am    Post subject: mysterious snippet Reply with quote


Hello everyone,

I'm new to this group hoping to get a little help.
To start, here is a condensed version of my current problem:

Can I use the the template class C as a template-parameter on the line
marked with (!!!)?

class A
{
public:
A(){;}
~A(){;}
template <class T> T getIt(T i){return i + i;}
};

template <class C>
class B
{
public:
B(){;}
~B(){;}
void nix()
{
A a;
int i = a.getIt<C>(4); //(!!!)
i = i;
}
};

int main()
{
B<int> b;
b.nix();
return 0;
}

The compiler I use is the gcc, version 3.3.5.
On the line marked with (!!!) it says:
"error: parse error before `;' token"
I like these errors that tell you absolutely nothing ;)

So, is this an problem of the language itself? Or is it just a compiler
issue and I am posting in the wrong group?

Many thanks for your help,

Klaus


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Alberto Ganesh Barbati
Guest
PostPosted: Tue Oct 18, 2005 9:33 pm    Post subject: Re: mysterious snippet Reply with quote


[email]khaeming (AT) web (DOT) de[/email] wrote:

Quote:

Can I use the the template class C as a template-parameter on the line
marked with (!!!)?

snip

The compiler I use is the gcc, version 3.3.5.
On the line marked with (!!!) it says:
"error: parse error before `;' token"
I like these errors that tell you absolutely nothing Wink


The code is correct and compiles on both VC7.1 and gcc 4.x. Looks like a
compiler bug. However, there's an easy fix, just change the offending
line to:

int i = a.template getIt<C>(4);
^^^^^^^^

the extra "template" keyword tells the compiler that getIt is a name of
a member template and not a regular member. As I said, the original code
is correct, so the keyword should not be needed in this context, because
"a" is a non-dependent name and the compiler can determine that getIt is
the name of a template. However, it seems that gcc 3.3.5 is not smart
enough and the extra help makes it happy. BTW, the .template syntax
*would* be needed if "a" were a dependent name because in that case the
compiler could not determine if the subsequent '<' would have to be
interpreted as a left angular bracket or as a less-than sign.

However, this raises an interesting question: is the .template syntax
allowed in this case? According to Vandevoorde and Josuttis' "C++
Templates", except for the case in which the .template syntax is
required, it's not allowed, although the standard isn't explicit about
that. However, both gcc 4.x and VC7.1 happily ignore the redundant
syntax. I like gcc and VC relaxedness here, it makes sense, but I feel
the standard should clarify the issue.

HTH,

Ganesh


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Bo Persson
Guest
PostPosted: Tue Oct 18, 2005 9:35 pm    Post subject: Re: mysterious snippet Reply with quote



<khaeming (AT) web (DOT) de> skrev i meddelandet
news:1129623826.546757.285530 (AT) g43g2000cwa (DOT) googlegroups.com...

Quote:
Hello everyone,

I'm new to this group hoping to get a little help.
To start, here is a condensed version of my current problem:

Can I use the the template class C as a template-parameter on the
line
marked with (!!!)?

class A
{
public:
A(){;}
~A(){;}
template <class T> T getIt(T i){return i + i;}
};

template <class C
class B
{
public:
B(){;}
~B(){;}
void nix()
{
A a;
int i = a.getIt i = i;
}
};

int main()
{
B<int> b;
b.nix();
return 0;
}

The compiler I use is the gcc, version 3.3.5.
On the line marked with (!!!) it says:
"error: parse error before `;' token"
I like these errors that tell you absolutely nothing ;)

So, is this an problem of the language itself? Or is it just a
compiler
issue and I am posting in the wrong group?


It seems to compile fine with other compilers, like MS and Comeau.
That makes 3.3.5 a suspect.


Bo Persson



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Victor Bazarov
Guest
PostPosted: Tue Oct 18, 2005 10:43 pm    Post subject: Re: mysterious snippet Reply with quote
[email]khaeming (AT) web (DOT) de[/email] wrote:
Quote:
I'm new to this group hoping to get a little help.
To start, here is a condensed version of my current problem:

Can I use the the template class C as a template-parameter on the line
marked with (!!!)?

class A
{
public:
A(){;}
~A(){;}
template <class T> T getIt(T i){return i + i;}
};

template <class C
class B
{
public:
B(){;}
~B(){;}
void nix()
{
A a;
int i = a.getIt

You probably need
int i = a. template getIt<C>(4);

Quote:
i = i;
}
};

[...]


V

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Ganny
Guest
PostPosted: Wed Oct 19, 2005 1:57 am    Post subject: Re: mysterious snippet Reply with quote
Quote:
int i = a.getIt<C>(4); //(!!!)
Change it to:

int i = a.template getIt<C>(4);

I've gcc 4.0 and the code works fine without explicit template
keyword....

Thanks!
-Ganesh


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Sumit Rajan
Guest
PostPosted: Wed Oct 19, 2005 2:00 am    Post subject: Re: mysterious snippet Reply with quote

<khaeming (AT) web (DOT) de> wrote


Quote:
class A
{
public:
A(){;}
~A(){;}
template <class T> T getIt(T i){return i + i;}
};

template <class C
class B
{
public:
B(){;}
~B(){;}
void nix()
{
A a;
int i = a.getIt i = i;
}
};

int main()
{
B<int> b;
b.nix();
return 0;
}

The compiler I use is the gcc, version 3.3.5.
On the line marked with (!!!) it says:
"error: parse error before `;' token"
I like these errors that tell you absolutely nothing Wink

The code looks okay to me. Besides, it seems to compile on Comeau C++, g++
3.4.2 and VC++ 7.1.

Regards,
Sumit.
--
Sumit Rajan <sumitr (AT) msdc (DOT) hcltech.com>



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Edson Manoel
Guest
PostPosted: Wed Oct 19, 2005 2:03 am    Post subject: Re: mysterious snippet Reply with quote
Msvc 7.1 compiled it ok. It can be a compiler issue, try this:

template <class C>
class B
{
public:
typedef typename C CType;
B(){;}
~B(){;}
void nix()
{
A a;
int i = a.getIt<CType>(4); //(!!!)
i = i;
}

};

Or this:

int i = a.getIt(4); //(!!!)


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Allan W
Guest
PostPosted: Wed Oct 19, 2005 8:34 am    Post subject: Re: mysterious snippet Reply with quote
[email]khaeming (AT) web (DOT) de[/email] wrote:
Quote:
To start, here is a condensed version of my current problem:
[SNIP]
Can I use the the template class C as a template-parameter on the line
marked with (!!!)?

Compiles without error on Microsoft Visual Studio .Net 2003.
Which doesn't prove it's legal... but I think it is.

Quote:
The compiler I use is the gcc, version 3.3.5.
On the line marked with (!!!) it says:
"error: parse error before `;' token"
I like these errors that tell you absolutely nothing Wink

Hmm, I don't use GCC but it has a better reputation than that.
Any chance you're compiling it as a C program, instead of a C++
program? Just a wild guess...

Quote:
So, is this an problem of the language itself? Or is it just a compiler
issue and I am posting in the wrong group?

Even if it's "just" a compiler issue, you can post questions here
about how to get it to compile portably.

Good luck.


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Abhishek Pamecha
Guest
PostPosted: Wed Oct 19, 2005 8:40 am    Post subject: Re: mysterious snippet Reply with quote
May be I dont understand your requirements but ..
Why would you need a template here? C seems obviously an integer (or it
cousins like long, unsigned int, long long, float etc /. Smile)

the conversion here should be handled automatically by the compiler if
you are not causing information loss. If you are causing information
loss, either this will only hide the problem or the compiler will warn
you while compiling.

In either case, I would not recommend this templatized approach unless
you have really diverse plans.


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