creating an array of a given template (c++)

Question

lately in my object oriented programming class we were dealing with templates.

in a question we got, we were asked to create a Queue class that can store any type
now my problem start when i want to store an array of somesort in this queue, for example:

Queue < char* >

now when i want to insert a new "node" to the queue i dont want to create a double pointing to a memory block. so basicly my question is: "how can i create an array of the same type of what the template class is pointing at?"

template<class T>
void Queue::enQueue(const T& value, int size = 1)
{
//exeptions handaling...
//handaling the case in wich the template is a pointer
if( _Is_pointer<T>() == true )
{
    T temp = new T[size]; // i know its a mistake but thats what i basicly mean to do
    for(int i = 0; i < size; i++)
        temp[i] = value[i];

    m_arr[++m_occupied] = temp; // m_arr is a data member of the T objects, m_occupied is as the name suggest
}

//...
}

thanks for the help :)

well i mean allocating one by a pointer, and its not necceraliy a 'char*' i mean any pointer — segal
– segal, Commented Jan 17, 2015 at 20:54
@segal Why do you differentiate between whether or not a pointer is passed? If I want a Queue<char *>, why not respect this and give me what I would expect? Why are you writing special code, just because the type I passed to you is a pointer? — PaulMcKenzie
– PaulMcKenzie, Commented Jan 17, 2015 at 20:57
well i do that because if i enqueue a ` char* ` for example and i delete it @PaulMcKenzie from the main i dont want to create double pointing, because when this queue will reach its d'tor ill basicly try to release memory i dont own anymore, though its true that i can do that to basiclly anything when i think about it now. ive down it after i wrote the code and done some stuff so i thought about all this thing afterwards — segal
– segal, Commented Jan 17, 2015 at 21:03
@segal - You're doing too much "hand-holding". If someone wants a Queue<char*>, let them worry about the char* and what it potentially points to. All your Queue class should worry about is its own memory, not the user's memory. For example, look at std::vector -- if someone wants a std::vector<char*>, vector does nothing special just because the type is a pointer. If you're writing special code just because the type is a pointer, then your implementation is flawed. — PaulMcKenzie
– PaulMcKenzie, Commented Jan 18, 2015 at 4:03

sehe · Accepted Answer · 2015-01-17 20:54:11Z

You could make template argument deduction work for you

// handling the case in wich the template is a pointer
template <class T> void Queue::enQueue(T const* value, int size = 1) {

This way, the overload deduces T as the type of object that value points at.

Now, you probably want to std::vector because you cannot treat arrays as simple values. Also, the use of new and delete for this kind of task is a code smell.

Guideline: In modern c++, vector<> is the default container for dynamically sized arrays, array<> for fixed-size arrays.

// handling the case in wich the template is a pointer
template <class T> void Queue::enQueue(T const* value, int size = 1) {
    m_arr[++m_occupied] = temp(value, value + size);
}

BONUS You can even deduce arrays with size, if you're passing true references to arrays:

// handling the case in wich the template is an array reference
template <class T, size_t Size> void Queue::enQueue(T const (&value)[Size]) {
    m_arr[++m_occupied] = std::vector<T>(value, value + Size);
}

Collectives™ on Stack Overflow

creating an array of a given template (c++)

1 Answer 1

Comments

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Related