Template as parameter in class - c++

Question

I have header file and in my header file I make a template and I want to use the template just on one function and not force all other functions. Is it possible to get the type before the function like i did in main?
This is an example:
TestTemp.h
// TestTemp.h
#ifndef _TESTTEMP_H_
#define _TESTTEMP_H_
template<class T>
class TestTemp
{
public:
TestTemp();
void SetValue( int obj_i );
int Getalue();
void sum(T b, T a);
private:
int m_Obj;
};
#include "TestTemp.cpp"
#endif
TestTemp.cpp
//TestTemp.cpp
include<TestTemp.h>
TestTemp::TestTemp()
{
}
void TestTemp::SetValue( int obj_i )
{
m_Obj = obj_i ;
}
int TestTemp::GetValue()
{
return m_Obj ;
}
template<class T>
void TestTemp<T>::sum(T b, T a)
{
T c;
c = b + a;
}
main.cpp
//main.cpp
include<TestTemp.h>
void main()
{
TestTemp t;
t.sum<int>(3,4);
}
Have any ideas?

Answer 1

Your TestTemp is a template class already, no need to make sum template function.
TestTemp<int> t;
t.sum(3, 4);
If you really want to make sum function a template function of TestTemp:
template<class T>
class TestTemp
{
public:
//....
template<typename U>
void sum(U b, U a);
private:
int m_Obj;
};
To implement it outside template class:
template<class T>
template<typename U>
void TestTemp<T>::sum(U b, U a)
{
T c;
c = b + a;
}
int main()
{
TestTemp<int> t;
t.sum<int>(3, 4);
}
However, I feel you just need a free template function
template<typename T>
T sum(T a, T b)
{ return a + b; }

Answer 2

// TestTemp.h
#ifndef _TEST_TEMP_H_
#define _TEST_TEMP_H_
class TestTemp
{
public:
TestTemp();
void SetValue( int obj_i );
int Getalue();
template<class T>
void sum(T b, T a);
private:
int m_Obj;
};
TestTemp::TestTemp() {}
void TestTemp::SetValue( int obj_i )
{
m_Obj = obj_i ;
}
int TestTemp::Getalue()
{
return m_Obj ;
}
template<class T>
void TestTemp::sum(T b, T a)
{
T c;
c = b + a;
}
#endif
//main.cpp
#include <TestTemp.h>
int main()
{
TestTemp t;
t.sum<int>(3,4);
return 0;
}
What you need is a normal class which has a template member function.
It's not a god idea to include an cpp file in header file. For template functions, just put it in header file.

Answer 3

You should take a look here. There are many examples.
I think it should work as you expect it if you just remove
template<class T>
from the
#ifndef _TESTTEMP_H_
#define _TESTTEMP_H_
--> template<class T> <--
class TestTemp
block. You don't have to define the whole class as templated when you just want a method to have template parameters.

Answer 4

You just need to define TestTemp as normal class of which "sum" is a template function. Then in your function "main" (i.e. the caller), the template argument will be deduced from the function arguments.
class TestTemp
{
public:
TestTemp();
void SetValue(int obj_i);
int Getalue();
template<class T>
void sum(T b, T a);
private:
int m_Obj;
};
TestTemp::TestTemp() {}
void TestTemp::SetValue(int obj_i)
{
m_Obj = obj_i;
}
int TestTemp::Getalue()
{
return m_Obj;
}
template<class T>
void TestTemp::sum(T b, T a)
{
T c;
c = b + a;
}
//main.cpp
int main()
{
TestTemp t;
t.sum(3, 4);
return 0;
}