Class template with array or vector arguments - c++

Question

I need to write a class template definition with two template parameters (type , functor) and two template arguments (array/std::vector , int) that can execute the following code:
const char* message= "Message";
const transform<char, firstFunctor> first(message, lengthOfMessage);
transform_view<int, secondFunctor> second(intArray, intSize);
transform<double, thirdFunctor> third(doubleArray, doubleSize);
The type of the array/ vector has to match the type of the first template parameter.
I tried some variations like this:
template <typename A, typename B>
class transform
{
public:
transform<A, B>(A[], B) {...};
}
But I could not get the constructor's first parameter to match all of the three types.
Any advice is appreciated, thanks!

Answer 1

you wrote the definition of the constructor incorrectly.
transform<A, B>(A[], B) {...}; you will pass a vector, so why did you write A[] as a parameter type?
You need something like the following
#include <iostream>
template <typename T>
struct functor{
void operator()(const T array [], size_t sze) {
for (int i{}; i < sze; ++i) {
std::cout << array[i] << " ";
}
std::cout << "\n";
}
};
template<typename T, typename Function>
class transform {
const T* array;
size_t sze;
Function functor{};
public:
transform(const T array [], size_t sze):array{array}, sze{sze}{
functor(array, sze);
}
};
template< typename T, typename E>
using transform_view = transform<T, E>;
int main()
{
using firstFunctor = functor<char>;
using secondFunctor = functor<int>;
using thirdFunctor = functor<double>;
const char *message = "Message";
size_t lengthOfMessage = 7;
int intArray[] = {1, 3};
size_t intSize = 2;
double doubleArray[] = {1.4, 3.2};
size_t doubleSize = 2;
//The given three lines
const transform<char, firstFunctor> first(message, lengthOfMessage);
transform_view<int, secondFunctor> second(intArray, intSize);
transform<double, thirdFunctor> third(doubleArray, doubleSize);
}
The output
M e s s a g e
1 3
1.4 3.2

Answer 2

From what I understand, the problem is the first parameter being the array in the template.
Try the following constructor:
transform(A* arr, B el){
//now here is a tricky part, because there is a very big difference
//between a char*, and an int/double/unsigned/float/... *.
}
If you have an array of the type A in the class and want to change it to the one passed:
private:
A* my_array;
you can try sth like this:
if(dynamic_cast<char*>(arr)) //if arr is of type char* {
if (this->my_array != nullptr) delete my_array; //not needed if in a basic constructor...
size_t len = strlen(arr);
my_array = new char [len + 1];
strcpy(this->my_array, arr); //(destination, source)
my_array[len] = '\0';
}
else //if it is a numeric array
{
this->my_array = arr;
//redirecting the pointers in enough
}
Oh and if you are on Visual Studio, strcpy will work if you write
'#pragma warning (disable: 4996)' at the top of the file.
Otherwise it marks it as unsafe and suggests strncpy, strcpy_s, ...