Explicit Template Argument Specification

[subi09]

i started reading about templates and i got confused on the below.

template<class T>

T max(T t1, T t2)
{

    int


   if (t1 > t2)
      return t1;
return t2;
}

int main(){

 std::cout<<max<int>(120,14.55);
  return 0;
}

o/p is 120 .But when i compiled the above i got the below warning.

warning:passing double for argument 2 to T max(T, T) [with T = int]. why this warning came is my question since i have already instantiated for T max(int t1,double t2).

Because as per my understanding here if i explicitly mention only one data type(here int),other would be deducted from the argument type(14.55) by the compiler.That means T max(T t1, T t2) instantiates T max(int t1,double t2)in this case.I read this concept from some template documents in internet.

Please clear my doubts.else i cant proceed further

[Lucaci Andrew]

The function header is this:

T max(T t1, T t2)

as for the actual parameters: (120,14.55); where 1 is an int, and the other is a double, thus the warning:passing double for argument 2 to T max(T, T) [with T = int].

You have the same type for the parameters as for the return value. So, if you privide arguments which are of different types you'll definitely get a warning (for numbers, since doubles/floats can be trunchated to ints, and ints converted to double/floats) and errors for other types.

If you declare your function like this:

#include <iostream>
using namespace std;
template <class T, class T1>
T1 maxs(T t1, T1 t2){
   if (t1 > t2)
      return (T1)t1;
   return t2;
}

int main(){
    cout<<maxs<int, double>(20, 4.6);
}

you will be able to have two types for that arguments, provided you declare them.
Template T is just a sort of macro for the compiler, which says that when the code will be run, every instance of the word T will be recplaced with the word given as the tempalte parameter when calling that function.

By your example, this would hold:

#include <iostream>
using namespace std;
template <class T>
T maxs(T t1, T t2){
   if (t1 > t2)
      return t1;
   return t2;
}

int main(){
    cout<<maxs<int>(20, 4)<<endl;
    cout<<maxs<double>(20.0, 20.1);
}

The same function, called once with int as the template parameter, and 2nd with double as the template parameter, acting in the same way.

[subi09]

Thanks for the reply