C / C++ / MFC

Member 4773877 wrote:

the example given is in the pie chart, how to do for the line graph?

George_George wrote:

2. if you agree with Bjarne's points, g(int) -- declaration only -- will instantise function f to f<int>,

George_George wrote:

could you also provide some code to prove please?

Rajkumar R wrote:

your example is quite enough to prove, just compile the code (don't build, i mean don't link), the code successfully compiles.

George_George wrote:

I think you mean the sample in my original question, right?

George_George wrote:

why if compile successful implies f is instantised by g(int) declaration other than f(2) inside h()?

George_George wrote:

During the time of instantiation or during the time of compiler parsing definition of template function f?

template<class T> void f(T) { }

template void f<int> (int);

Rajkumar R wrote:

And question, declaration of g() will instantise f<int> (T) is true. since g is non inline non template function.

try commenting the declaration of g(); you will get compilation error, identifier g, not found when instantiating funtion void f<int>(T), otherwise not; this is the proof.

template <class T> void f(T a) {g (a);}

void g (int a);

George_George wrote:

the point of instantiation for f<int>() is just before h(), so the g() called in f() is the global g (int) rather than the local g (double).
--------------------

BTW: from above statement from Bjarne, I think he means declaration of g(int) before h() will instiatise f to f <int>.

1>------ Build started: Project: test_template4, Configuration: Debug Win32 ------
1>Compiling...
1>main.cpp
1>d:\visual studio 2008\projects\test_template4\test_template4\main.cpp(15) : error C2955: 'Base' : use of class template requires template argument list
1>        d:\visual studio 2008\projects\test_template4\test_template4\main.cpp(5) : see declaration of 'Base'
1>        d:\visual studio 2008\projects\test_template4\test_template4\main.cpp(21) : see reference to class template instantiation 'Derived<T>' being compiled
1>d:\visual studio 2008\projects\test_template4\test_template4\main.cpp(15) : error C2955: 'Base' : use of class template requires template argument list
1>        d:\visual studio 2008\projects\test_template4\test_template4\main.cpp(5) : see declaration of 'Base'
1>        d:\visual studio 2008\projects\test_template4\test_template4\main.cpp(26) : see reference to class template instantiation 'Derived<T>' being compiled
1>        with
1>        [
1>            T=int
1>        ]

#include <iostream>

using namespace std;

template <typename T> struct Base {
public:	
	Base (int _i): i (_i)
	{

	}

	int i;
};

template <typename T> struct Derived : public Base/*<T>*/ {
public:
	Derived (int _i) : Base<T> (_i)
	{
	}
	int get_i() { return i; }
};


int main()
{
	Derived<int> d (200);
	cout << d.get_i() << endl; // output 200
	return 0;
}

George_George wrote:

Is there some new rules we do not cover theses days about instantiation of template class?

"No code is generated for a templated class or function until it is instantiated. 
Moreover, member functions are instantiated only if they are called"

George_George wrote:

What is your answer and comments to my question (1) in the original reply?

George_George wrote:

And why you make such answer?

f(char) { printf_s("f(char)\n");

g('c');

George_George wrote:

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