如何为两种或更多数据类型创建 function 模板？

Question

I want to use function templates with two or more data types. So I made a example, which gets two 'T' type data then return 'T1' type data. Here is code:

#include <iostream>
using namespace std;
template <typename T, typename T2> T get(T2 a, T2 b)
{
    if (a < b)
        return b;
    else
        return a;
}

int main()
{
    cout << get<float, int>(10.2, 20.3);
}

I want that this code returns the larger of the two 'int-type' numbers to the 'float' type. Namely I expected the result to '20.0'. But the result is 20. I can not understand why the result's type is 'int'. Please correct my code to return 'float' type, '20.0'. Namely I wonder how to specify the data type of the return value if the input factor and return value are different.

Answer 1

Your code is perfectly fine, given the strange cast of inputs to int . Look at the output of:

#include <iostream>
#include <boost/type_index.hpp>
using namespace std;
using boost::typeindex::type_id_with_cvr;

template <typename T, typename T2> T get(T2 a, T2 b)
{
    if (a < b)
        return b;
    else
        return a;
}

int main()
{
  float test = 20.0;
  
  cout << get<float, int>(10.2, 20.3) << " "
       << type_id_with_cvr<decltype(get<float,int>(10.2,20.3))>().pretty_name() << endl;
  cout << test << endl;
}

which is

20 float
20

so, of course, the return type of your function IS float, the output is just how cout will show this to you. But you know, you can highly customize how cout prints out your data with #include <iomanip> .