Template class constraint template function problem-CodePudding

Procedure 1:
#include
Using STD: : cout;
Using STD: : endl;
Template Void show2 (T & amp; Hf) {STD: : coutTemplate
Class A
{
Private:
int a;

Public:
Friend void show2 & lt; T> (A & amp;);
};

The template class A;
Int main (void)
{

return 0;
}
Results: the error

Program 2:
#include
Using STD: : cout;
Using STD: : endl;
Template Void show2 (T & amp; Hf) {STD: : coutTemplate
Class A
{
Private:
int a;

Public:
Friend void show2 & lt; T> (A & amp;);
};

//the template class A;
Int main (void)
{

return 0;
}
Results: no error

Is the difference between the two procedures: there are explicit instantiation is an error, otherwise we are not an error, what reason is this?

CodePudding user response:

Your explicit instantiation grammar is wrong?

CodePudding user response:

Both are wrong, the second is not an error because you haven't instantiate
Template class a friend is such statement

 # include 
#include 
using namespace std; 

Template 
Class A 
{
Private: 
int a; 

Public: 
A () {} 
Template 
Friend void show2 (A & amp;); 
}; 


Template 
Void show2 (A & Hf) 
{
STD: : cout & lt; } 
Template<> 
The class A {
Double a; 
Public: 
(A) {A=0; } 
Template 
Friend void show2 (A & amp;); 
}; 
Int main (void) 
{
A A1. 
Show2 (a1); 
return 0; 
}