用于将指针传递给模板化函数的语法

Question

One version of my code works. Another (which I would have thought was preferable) fails to compile. If I declare the simple pair of functions:

template<class T>
void pass_function(T (*func))
{
  cout << func() << endl;
}

double func_to_pass()
{
  return(0);
}

I can call

pass_function(&func_to_pass);

and everything works as expected. I know that it is "figuring out" that the template is standing for a double here even though I haven't told it that it is a double in this call.

But, if instead I call

pass_function<double>(&func_to_pass);

I, naively, would think this would be better since I am trying to tell it that the function passed as the argument will return a double. But I get the error:

error: no matching function for call to ‘pass_function(double (*)())’

So, clearly I am misunderstanding something about the syntax of using templates.

Answer 1

Change the definition like

template<class T>
void pass_function(T (*func)())
{
  cout << func() << endl;
}

Otherwise when you explicitly specify the template argument the function is specialized like

void pass_function( double  * );