illegal use of this type as an expression

[hsuch]

Hi all, I'm new to C++. I've a stupid problem. This is the code I used: class A { int x; }; class B { template<class T> void temp(void){ }; void test(void); }; void B::test(void) { temp<A>(); }; Why can't I compile this code? The error message is: test.cpp(23) :error C2275: 'A' : illegal use of this type as an expression test.cpp(23) : error C2059: syntax error : ')' If I move the template function temp() out from class B, then it is ok. Could someone help me? Thanks a lot.

[Sceptic Mole]

Which compiler do you use?

[Chris Losinger]

it works fine in VS 2005, but fails in VC6. not sure why it fails.

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[David Crow]

Are you wanting something like:

class A
{
int x;
};

class B
{
template<class T> void temp(const T& data){ }
void test(void);
};

void B::test(void)
{
A a;
temp(&a);
};

---

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[Michael Dunn]

VC6 has problems when a template type parameter doesn't appear in the function's parameter list, as is the case in hsuch's sample code. The usual workaround is to add a dummy T* param that defauls to NULL.

--Mike-- Visual C++ MVP :cool: LINKS~! Ericahist | PimpFish | CP SearchBar v3.0 | C++ Forum FAQ Ford, what's this fish doing in my ear?

[Michael Dunn]

If you're using VC6, change it to

template<class T> void temp(T* = NULL) { }

to work around a compiler bug.

--Mike-- Visual C++ MVP :cool: LINKS~! Ericahist | PimpFish | CP SearchBar v3.0 | C++ Forum FAQ Ford, what's this fish doing in my ear?

[Chris Losinger]

you mean like this?

class A
{
int x;
};

class B
{
template < class T > void temp(T *)
{
}
void test(void);
};

void B::test(void)
{
A z;
temp< A >(&z);
};

that doesn't work either. edit: adding the "T* = NULL" works, though

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[Michael Dunn]

See my response below.

--Mike-- Visual C++ MVP :cool: LINKS~! Ericahist | PimpFish | CP SearchBar v3.0 | C++ Forum FAQ Ford, what's this fish doing in my ear?

[hsuch]

Sorry for missing the platform. I use VC6.0. I also try on VC Express, it is ok. So, it is compiler problem?

[hsuch]

class A
{	
	int x;
};
class B
{	
	template<class T> void temp(T* = NULL){}	
	void test(void);
};
void B::test(void)
{ 	
	temp<A>();  
};

Still doesn't work. :(