I have a code:
var *item[8] = { nullptr };
and it works good. But i need to do this dynamically. This is what i tried:
int n = 8;
var **item;
item = new var*[n]();
item = { nullptr };
but this is not working. Where is the difference and what should i do?
//Sorry for my english
The () in item = new var*[n](); will value-initialize all of the pointers to nullptr for you, so you don't need to do it manually afterwards.
int n = 8;
var **item;
item = new var*[n](); // <-- all are nullptr here
That said, you really should be using std::vector instead of new[] directly:
int n = 8;
std::vector<var*> item;
item.resize(n);
Or simply:
int n = 8;
std::vector<var*> item(n);
Either way should initialize the pointers to nullptr as well. But if you want to be explicit about it, you can do so:
int n = 8;
std::vector<var*> item;
item.resize(n, nullptr);
int n = 8;
std::vector<var*> item(n, nullptr);
if you have an array, vector or a container in general and you want to fill it with some value whichever that is you can use the std::fill function:
std::fill(item,item+n,nullptr);
However if you want to assign nullptr at initialization time, it is much easier: you use zero initialization and you are fine. Just be aware of the difference between zero and default initialization:
item = new var*[n]{}; //zero initialized (all elements would have nullptr as value)
item = new var*[n]; //default initialized (elements might not have nullptr as value)
item = new var*[n](); //default initialized until C++03
//zero initialized after C++03
Anyway, I would suggest you to migrate to std::vector instead of C style arrays. You generally end up with much less error-prone code.
{ }only initialises the first element. This is a common misconception, where people thinkbool arr[5] = { true };will initialise them all totrue