What does asterisk before brackets on object creation mean in C++?

Question

I was reading an example of a hash table implementation in C++ from a website and saw this.

private:
  HashEntry **table;
public:
  HashMap() {
        table = new HashEntry*[TABLE_SIZE];
        for (int i = 0; i < TABLE_SIZE; i++)
              table[i] = NULL;
  }

The line with the syntax I don't understand is:

table = new HashEntry*[TABLE_SIZE];

What does it mean to have the asterisk before the brackets like that?

well it means it's an array of `HashEntry*` of size `TABLE_SIZE` — Marson Mao, Feb 05 '15 at 05:57
you can read this for some reference http://stackoverflow.com/questions/16001803/pointer-to-pointer-dynamic-two-dimensional-array — Marson Mao, Feb 05 '15 at 05:59

score 5 · Accepted Answer · answered Feb 05 '15 at 06:02

5

new HashEntry*[TABLE_SIZE] allocates and constructs an array of TABLE_SIZE elements, where each element is a HashEntry*, i.e. a pointer to a HashEntry.

A more modern C++ version of that would be:

private:
  std::vector<std::unique_ptr<HashEntry>> table;
public:
  HashMap() : table(TABLE_SIZE) {}

This avoids having to define your own destructor, and is generally safer.

answered Feb 05 '15 at 06:02

John Zwinck

239,568
38
324
436

And automatically sets everything in it to NULL I assume? – James4701 Feb 05 '15 at 06:11
@James4701: unique_ptr (and other smart pointers generally) is "null" by default, yes. This is contrary to raw C pointers which are uninitialized by default. – John Zwinck Feb 05 '15 at 06:25

score 0 · Answer 2 · answered Feb 05 '15 at 06:12

0

The asterisk indicates that it is a pointer

Here are some links

http://www.cprogramming.com/tutorial/c/lesson6.html

http://www.tutorialspoint.com/cplusplus/cpp_pointers.htm

http://www.augustcouncil.com/~tgibson/tutorial/ptr.html

answered Feb 05 '15 at 06:12

Arun A S

6,421
4
29
43

What does asterisk before brackets on object creation mean in C++?

2 Answers2