Template function overloading. Understanding char - c++

Question

I have a simple code that compares couple values. I'm using template function to reduce the amount of code, so i overloaded function twice(for different cases).
//cmp.h
template <class T>
bool cmp(T x,T y)
{
if(x == y)
{
return true;
}else
return false;
}
template <class T>
bool cmp(T *x,T *y)
{
if(*x==*y)
{ return true;}else
return false;
}
//main.cpp
#include <iostream>
#include <string>
#include "cmp.h"
using std::cout;
using std::endl;
using std::string;
int main() {
int aInt = 1, bInt = 2;
double aDouble = 3.0, bDouble = 3.0;
char aChars[5] = "haha", bChars[5] = "hahb";
char taChars[6] = "trick", tbChars[6] = "trick";
string aStr = "haha", bStr = "aha";
int* aIntPtr = &aInt, *bIntPtr = &bInt;
cout << cmp(aInt, bInt)<< endl;
cout << cmp(aDouble, bDouble)<< endl;
cout << cmp(aChars, bChars)<< endl;//i can't figure out why char prints out true here ???
cout << cmp(taChars, tbChars)<< endl;
cout << cmp(aStr, bStr)<< endl;
cout << cmp(aIntPtr, bIntPtr)<< endl;
cout << cmp(&aDouble, &bDouble) << endl;
return 0;
}
My output is:
0
1
1
1
0
0
1
And i expected:
0
1
0
1
0
0
1
Why it shows that two strings are identical ? Why if i entirely change the word, lets say
char aChars[5] = "jack", bChars[5] = "hahb";
then only it gives the right result. Isn't my second overloaded function should handle this right? (bool cmp(T *x,T *y))

Answer 1

Why it shows that two strings are identical ?
Because
template <class T>
bool cmp(T *x,T *y)
{
if(*x == *y)
{
return true;
}else
return false;
}
check only the first value pointed by x and y.
So when you check
char aChars[5] = "haha", bChars[5] = "hahb";
cout << cmp(aChars, bChars)<< endl;//
check that h is equal to h.
If you want check the equality between strings (and if you want avoid the use of the good-old std::strcmp()) you have to check all characters until the first zero.
But this is true for old style C-string; I don't think it's a good idea to develop a function that check equality between pointer for a generic type T.
-- EDIT --
Could u guide me please
To give an example... it's a lot of time that I don't think in plain C but something as follows should works
bool cmp (char const * p1, char const * p2)
{
for ( ; *p1 && *p1 == *p2 ; ++p1, ++p2 )
;
return *p1 == *p2;
}
Off Topic: you write code as
bool cmp(T *x,T *y)
{
if(*x==*y)
{ return true;}else
return false;
}
It's equivalent to
bool cmp(T *x,T *y)
{ return *x == *y; }
More generally speaking... if you have a code of type
if ( someTest )
return true;
else
return false;
and the function return a bool (or someTest is of type bool), you can write (and, IMHO, is more readable and elegant) simply write
return someTest;

Answer 2

Why it shows that two strings are identical ?
Array decays to pointer, so char taChars[6] will use overload template <class T>
bool cmp(T *x,T *y) and so compare only first element (which are equal in your case).
In C++17, you might do:
template <typename T>
bool cmp(const T& lhs, const T& rhs)
{
if constexpr (std::is_pointer<T>::value) {
return *lhs == *rhs;
} else if constexpr (std::is_array<T>::value) {
return std::equal(std::begin(lhs), std::end(lhs), std::begin(rhs), std::end(rhs));
} else {
return lhs == rhs;
}
}
Demo