Template classes and initializing an array to zero

Question

I posted earlier today about template classes, but was pretty far off and got a solution to my previous problem from here. Of course when that's dealt with, there's always a new one that I can't seem to figure out.

Given the following constructor:

template <typename Type, int inSize>
sortedVector<Type, inSize>::sortedVector():
    size(inSize), vector(new Type[inSize]), amountElements(0)
{}

I want to make a dynamic array, which I then can insert elements of whatever type into via an add-method. The calls from main will look as follows:

sortedVector<Polygon, 10> polygons;
sortedVector<int, 6> ints;

How can I initialize the array to zero when it's constructed? I can not set an object to zero ;)

I thought I was being smart and tried to overload the =-operator for Polygon and given an int it would do nothing. Turns out I can not do that ):

Any good suggestions?

Also, here's the template class sortedVector:

template <typename Type, int inSize>
class sortedVector
{
public:
    sortedVector();
    int getSize();
    int getAmountElements()
    bool add(const Type &element);

private:
    Type *vector;
    int size;
    int amountElements;
};

and just in case also Polygon:

class Polygon
{
public:
    Polygon();
    Polygon(Vertex inVertArr[], int inAmountVertices);
    ~Polygon();
    void add(Vertex newVer);
    double area();
    int minx();
    int maxx();
    int miny();
    int maxy();
    int getAmountVertices() const;        
    friend bool operator > (const Polygon &operand1, const Polygon &operand2);
    friend bool operator < (const Polygon &operand1, const Polygon &operand2);

private:
    Vertex *Poly;
    int amountVertices;
};

Here's some advice: Add the homework tag to your question if it involves a homework assignment. Otherwise you'll get lots of "use std::vector" type of answers. — Emile Cormier
– Emile Cormier, Commented Mar 18, 2012 at 16:59

Emile Cormier · Accepted Answer · 2012-03-18 16:49:38Z

4

Initialize the array elements to Type(). This is what the standard library containers do. For built-in numeric types, Type() is equivalent to 0. For class/struct types, Type() constructs a temporary default-constructed object.

edited Mar 18, 2012 at 16:49

answered Mar 18, 2012 at 16:41

Emile Cormier

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Comments

Dietmar Kühl · Accepted Answer · 2012-03-18 16:48:40Z

2

You can just use Type() to get a default constructed object. A better approach is to use std::vector<T> either directly or via a thin wrapper adding whatever functionality or constraints are needed. Although it is doable without std::vector<T> any solution which actually properly manages resources and objects will end up reimplementing at least parts of std::vector<T>.

answered Mar 18, 2012 at 16:48

Dietmar Kühl

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6 Comments

Emile Cormier Over a year ago

+1 Wrapping a std::vector<T> instead of re-inventing the wheel is good advice.

Emile Cormier Over a year ago

I checked the OP's previous questions and this seems to be part of an assignment. They often forbid the use of STL containers in programming classes, so that students learn how to program their own data structures from scratch.

JKase Over a year ago

It'd probably be good, but as you said Emile - restrictions :)

Dietmar Kühl Over a year ago

This, unfortunately, shows the ignorance of teachers and or the inability to set appropriate assignment (probably both plus a number of other non-favourable personal traits).Creating a template container isn't hard but asking students to do it who need to ask how to get a zero value just exercises bad practices. I stick with the advice to use std::vector<T>.

Emile Cormier Over a year ago

@DietmarKühl : If there weren't any restrictions, how could you give an assignment to implement, say, a linked list in a data structures class? I agree that once students learn basic data structures, they should be taught to use standard library containers/algorithms whenever possible. :-)

|

John Zwinck · Accepted Answer · 2012-03-18 16:42:36Z

0

Just assign every element of the "vector" (confusing name, by the way, given the prominence of std::vector<>) to the default value. The default value is just Type(), so you'd do something like this in the constructor body:

std::fill(vector, vector + size, Type());

answered Mar 18, 2012 at 16:42

John Zwinck

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Comments

Dmitriy Kachko · Accepted Answer · 2012-03-18 16:42:55Z

0

How can I initialize the array to zero when it's constructed? I can not set an object to zero ;)

You can use so-called default constructed value. In other words, you need to define (if it is not defined) special value that will play role of zero for your object.

answered Mar 18, 2012 at 16:42

Dmitriy Kachko

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