Question

I face a problem similar to this one.

int j = 6;
int *k = new int[j]{4};

The warning is :

warning: non-constant array size in new, unable to verify length 
of initializer-list [enabled by default]

I face only a warning, no errors and I run with -std=gnu++11

Plus, I want the constructor called for every instance. If I print the array values, all

Answer 1

The problem is exactly what the compiler is telling you.

The dimension is known only at runtime, so you may only use runtime functionality, such as:

std::vector<int> v(j, 4);
// `v` contains `j` ints, all initialised to `4`

If you have an element type that cannot be default-constructed, you may construct the elements in-place:

std::vector<T> v;
v.reserve(j);
for (size_t i = 0; i < j; i++)
   v.emplace_back(ctor-args-here);

You could probably also use an initializer list:

std::vector<T> v{
   T(ctor-args-here), T(ctor-args-here), T(ctor-args-here),
   T(ctor-args-here), T(ctor-args-here), T(ctor-args-here)
};

and the objects will be moved or, at worst, copied.

The point here is that vector elements don’t need to be default-constructible.

(Unfortunately I’m not aware of a way to do this without the loop or code repetition.)