function template specialization problem

function template specialization problem

[rodolfo]

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Hi, I don't know if this is a C++ or g++ problem, but this snippet
doesn't compile, but I think it should:

template <class T> void test(const char *par);

template <> void test<int>(const char *par = 0) {}

int main()
{
    test<int>();
}

g++ 3.4.5 returns the following errors:
test.cpp:3: error: default arguments are only permitted for function parameters
test.cpp:7: error: no matching function for call to `test()'

Well, the first error text is a little bit misleading because I'm
defining a default argument for a function parameter, but somehow this
is not parsed correctly, and g++ thinks it's not a function.

So, is this allowed in c++ or is a g++ parse bug?

Thanks,
Rodolfo Lima.

	

	
		
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Re: function template specialization problem

[Andrew Haley]

rodolfo@rodsoft.org writes:
 > Hi, I don't know if this is a C++ or g++ problem, but this snippet
 > doesn't compile, but I think it should:
 > 
 > template <class T> void test(const char *par);
 > 
 > template <> void test<int>(const char *par = 0) {}
 > 
 > int main()
 > {
 >     test<int>();
 > }
 > 
 > g++ 3.4.5 returns the following errors:
 > test.cpp:3: error: default arguments are only permitted for function parameters
 > test.cpp:7: error: no matching function for call to `test()'
 > 
 > Well, the first error text is a little bit misleading because I'm
 > defining a default argument for a function parameter, but somehow this
 > is not parsed correctly, and g++ thinks it's not a function.
 > 
 > So, is this allowed in c++ or is a g++ parse bug?

No.  See Section 14.7.3, Para. 21.

"Default function arguments shall not be specified in the explicit
specialization of a function template."

Andrew.

Re: function template specialization problem

[Daniel Llorens del Río]

On 21 Mar, 2006, at 20:16, rodolfo@rodsoft.org wrote:

> Hi, I don't know if this is a C++ or g++ problem, but this snippet
> doesn't compile, but I think it should:
>
> template <class T> void test(const char *par);
>
> template <> void test<int>(const char *par = 0) {}
>
> int main()
> {
>     test<int>();
> }
>
> g++ 3.4.5 returns the following errors:
> test.cpp:3: error: default arguments are only permitted for  
> function parameters
> test.cpp:7: error: no matching function for call to `test()'

The first error message is unclear, but the code is illegal anyway.  
You cannot declare a default parameter in a specialization. You must  
declare it in the function template declaration, and only there.