显式实例化模板方法中的编译错误

Question

I've two different template classes. One of them has a member function that returns a pointer to an object of the other template class. Currently, I'm not able to compile the code below and any suggestions are really welcome.

main.cpp

#include <stdio.h>
#include <stdlib.h>
#include <foo.h>
#include <bar.h>

int main(int argc, char **argv){
    ...
    int nParam;
    ...

    CFoo<float> * pFoo = NULL;
    pFoo = new CFoo<float>();

    CBar<float> * pBar = NULL;
    pBar = pFoo->doSomething(nParam); // error: no matching function for call to ‘CFoo<float>::doSomething(int)’

    ...

    delete pFoo;
    delete pBar;

    return (0);
}

foo.h

#include <bar.h>

template < class FOO_TYPE >
class CFoo{

    public:

        ...

        template < class BAR_TYPE >
        CBar<BAR_TYPE> * doSomething(int);
        ...
};

foo.cpp

template < class FOO_TYPE >
template < class BAR_TYPE >
CBar<BAR_TYPE> * CFoo<FOO_TYPE>::doSomething(int nParam){
    ...
}
#include "foo-impl.inc" 

foo-impl.inc

template class CFoo<float>;
template class CFoo<double>;

template CBar<float>* CFoo<float>::doSomething( int );
template CBar<double>* CFoo<float>::doSomething( int );
template CBar<double>* CFoo<double>::doSomething( int );
template CBar<float>* CFoo<double>::doSomething( int );

/*
I also tried the explicit instantiation in the last line, but I get the error below:
template-id ‘doSomething<CBar<float>*>’ for ‘CBar<float>* CFoo<float>::doSomething(int)’ does not match any template declaration
*/
// template CBar<float>* CFoo<float>::doSomething < CBar<float> * > ( int ); 

Consider that I need to call the doSomething method inside of a member function of a third class.

myclass.cpp

template < class FOO_TYPE, class BAR_TYPE >
void CMyClass<FOO_TYPE, class BAR_TYPE>::doSomeWork(CFoo<FOO_TYPE> * pFoo){
    ...
    int nParam;
    ...
    CBar<BAR_TYPE> * pBar = NULL;
    pBar = pFoo->doSomething<BAR_TYPE>(nParam); //error: expected primary-expression before ‘>’ token

    delete pBar;
    ...
} 

Note that, I had a similar problem that I posted a while ago in this forum , but by trying to adapt the suggestion to my code, I couldn't solve the bug. I hope, my post is valid.

Answer 1

The compiler can't deduce the template arguments -- it doesn't know whether you want to call CFoo<float>::doSomething<float>(int) , CFoo<float>::doSomething<unsigned int>(int) , or whatever. So, you have to explicitly tell it what the template arguments are:

// Explicitly call the function with BAR_TYPE=float
pBar = pFoo->doSomething<float>(1);