problem encountered by calling constructors explicitly.

Tarun Jha

here in the below program i have tried to pass the values of 1d matrix to the object of class Vector by using constructor explicit call.

#include
using namespace std;

const int size = 3;
class Vector {
int *v;

public:
Vector(){
v = new int[size];
for(int i=0; iv[i] * y.v[i] ;
return sum;
}

void display(){
    for(int i=0; i

Quote:

cout << "v1 = ";
v1.display();

cout << "v2 = ";
v2.display();

the above portion of code doesn't works as expected it gives,

Output:

Quote:

6 3 9
6 3 9
v1 = 6 3 9
v2 = 6 3 9
v1 x v2 = 126

Expected:

Quote:

Quote:

1 2 3
6 3 9
v1 = 1 2 3
v2 = 6 3 9
v1 x v2 = 39

Thank you

Joe Woodbury

The program shouldn't run as is. In your second constructor, you aren't allocating the memory for the vector. (You also aren't deleting that memory in a destructor.) Also note that you construct the v object in the default constructor. Since there is no assignment operator AND the second constructor is not marked explicit, it is creating a second instance of Vector and then member-wise copying that to the first, clobbering the allocation of v in the first instance. (Why your compiler is letting you get away with this is a mystery to me.) So, add a destructor and then put "explicit" in front of the second constructor. Then, remove the assignments and replace the declaration line with: v1(x), v2(y). (It's still messy code, but in a debugger, you can now see how you are explicitly calling the second constructor and never the first.)

Tarun Jha

thank you

CPallini

Since you know at compile time the array size, why don't you allocate it on the stack?

#include #include using namespace std;

constexpr size_t SIZE = 3;

class Vector
{
array x{};

public:
Vector (const array & a)
{
for (size_t n=0; n x{1,2,3};
array y{6,3,9};

Vector v1{x};
Vector v2{y};

cout << "v1 " << v1 << endl;
cout << "v2 " << v2 << endl;
cout << "v1*v2 = " << (v1*v2) << endl;
}