CODEWITHSUNDEEP
c++dynamic-arrays
haris
haris

Reputation: 2033

No array allocated using new can have an initializer?

In the book I am reading at the moment (C++ Complete Reference from Herbert Schildt), it says that no array allocated using new can have an initializer.

Can't I initialize a dynamically allocated array using new? If not whats the reason for it?

Upvotes: 12

Views: 6431

Answers (3)

CB Bailey
CB Bailey

Reputation: 792497

That's not quite true (you should almost certainly get yourself an alternative reference), you are allowed an empty initializer (()) which will value-initialize the array but yes, you can't initialize array elements individually when using array new. (See ISO/IEC 14882:2003 5.3.4 [expr.new] / 15)

E.g.

int* p = new int[5](); // array initialized to all zero
int* q = new int[5];   // array elements all have indeterminate value

There's no fundamental reason not to allow a more complicated initializer it's just that C++03 didn't have a grammar construct for it. In the next version of C++ you will be able to do something like this.

int* p = new int[5] {0, 1, 2, 3, 4};

Upvotes: 19

RoundPi
RoundPi

Reputation: 5947

I think the book is correct, in generally you cannot do that with current version of c++. But you can do that with boost::assign to achieve a dynamic array, see below

#include <boost/assign/list_of.hpp>
class Object{
public:
    Object(int i):m_data(i){}
private:
    int m_data;
};

int main()
{
    using namespace boost::assign;
    std::vector<Object> myvec = list_of(Object(1))(Object(2))(Object(3));
}

Upvotes: 0

iammilind
iammilind

Reputation: 70030

The book is correct; you cannot have,

int *p = new int[3](100);

There is no understandable reason behind it. That's why we have initializers for array in C++0x.

Upvotes: 0

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