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// test.cpp
#include <iostream>
 
using namespace std;
 
struct box {
    char maker[40];
    float height;
    float width;
    float length;
    float volume;
};
 
 
template <typename T>
T max(T a, T b) {
    return a > b ? a : b;
}
template <> box max<box>(box a, box b) {
    return a.volume > b.volume ? a : b; 
}
 
int main() {
    box b = {"Cube", 2.3F, 1.5f, 4.1f, 32.0f};
    box c = {"Box", 2.6f, 2.3f, 1.2f, 26.8f};
    int i1 = 5, i2 = 3;
 
    b = max(b, c);
    cout << max(i1, i2) << endl;
    cout << b.volume << endl;
 
    return 0;
}
 

prog.cpp: In function ‘int main()’:
prog.cpp:28:17: error: call of overloaded ‘max(box&, box&)’ is ambiguous
     b = max(b, c);
                 ^
prog.cpp:19:17: note: candidate: ‘T max(T, T) [with T = box]’
 template <> box max<box>(box a, box b) {
                 ^~~~~~~~
In file included from /usr/include/c++/8/bits/char_traits.h:39,
                 from /usr/include/c++/8/ios:40,
                 from /usr/include/c++/8/ostream:38,
                 from /usr/include/c++/8/iostream:39,
                 from prog.cpp:2:
/usr/include/c++/8/bits/stl_algobase.h:219:5: note: candidate: ‘constexpr const _Tp& std::max(const _Tp&, const _Tp&) [with _Tp = box]’
     max(const _Tp& __a, const _Tp& __b)
     ^~~
prog.cpp:29:23: error: call of overloaded ‘max(int&, int&)’ is ambiguous
     cout << max(i1, i2) << endl;
                       ^
prog.cpp:16:3: note: candidate: ‘T max(T, T) [with T = int]’
 T max(T a, T b) {
   ^~~
In file included from /usr/include/c++/8/bits/char_traits.h:39,
                 from /usr/include/c++/8/ios:40,
                 from /usr/include/c++/8/ostream:38,
                 from /usr/include/c++/8/iostream:39,
                 from prog.cpp:2:
/usr/include/c++/8/bits/stl_algobase.h:219:5: note: candidate: ‘constexpr const _Tp& std::max(const _Tp&, const _Tp&) [with _Tp = int]’
     max(const _Tp& __a, const _Tp& __b)
     ^~~

Standard output is empty