Constructor with array as argument

[eggsandbacon]

Hi,

Quick question. If I wanted to make a constructor that takes 2 arguments, an array of ints to copy into a vector and another int that tells me how many elements are in the array, how would I do this?

Assuming class name is OneTwo...

Would the constructor declaration be OneTwo(int, int) ?
Not sure how to take an array as an argument.

Also, once I do it, how do I copy the values into a new array that is dynamically allocated. Thanks

[bcrawford]

For the constructor declaration you would use :

OneTwo(int array[], int size);
or you don't have to declare name for the arguments
OneTwo(int [], int);

as for how to copy into a vector, use a for loop and check out the references here on this site for vectors. You'll have to use the vector member function push_back().

[JLBorges]

#include <vector>
#include <initializer_list> // C++11 only

struct A
{
    A() {} // 1. initialize to empty vector

    // 2. initialize to a vector of size n, each element being v
    A( std::size_t n, int v = 0 ) : sequence(n,v) {}

    // 3. initialize from pointer to first element of int array and its size
    A( const int* a, std::size_t n ) : sequence( a, a+n ) {}

    // 4. initialize from a polymorphic sequenceuence abstracted away with iterators
    template< typename ITERATOR >
    A( ITERATOR begin, ITERATOR end ) : sequence(begin,end) {}

    // 5. initialize from array via initializer list  - C++11 only
    A( std::initializer_list<int> ilist ) : sequence(ilist) {}

    //  6. initialize from array with compatible type
    template< typename T, std::size_t N > A( T(&a)[N] ) : sequence( a, a+N ) {}

    std::vector<int> sequence ;
};

int main()
{
    A a1 ; // 1

    A a2( 10U, 99 ) ; // 2

    const int a[] = { 0, 1, 2, 3, 4 } ;
    A a3( a, sizeof(a)/sizeof(int) ) ; // 3

    const short b[] = { 5, 6, 7, 8 } ;
    A a4( b, b + sizeof(b)/sizeof(short) ) ; // 4

    A a5 = { 10, 11, 12, 13, 14, 15, 16 } ; // 5

    A a6(b) ; // 6
}

[Cubbi]

If you're taking in an array, you don't need an extra size argument, because the size is part of the array's type already:

#include <vector>
struct One
{
    std::vector<int> data;
    template<std::size_t N>
    One(const int (&a)[N]) : data(a, a+N) {}
};

I am guessing you meant to say pointer to the first element of an array and the size:

struct Two
{
    std::vector<int> data;
    Two(const int* a, std::size_t n) : data(a, a+n) {}
};

int main()
{
    int a[5] = {1,2,3,4,5};
    One o(a);
    Two t(a, 5);
}

edit: I am slow today!

[JLBorges]

> If you're taking in an array, you don't need an extra size argument, because the size is part of the array's type already

Yes. I'm correcting it now, thanks.