CODEWITHSUNDEEP
c++pointersarray-initialization
Woody1193
Woody1193

Reputation: 7960

C++ Initializing Array of Pointers

I know with pointers you can do this:

T * myPtr = 0;

which sets the pointer to a NULL value. However, when I try to do this:

T * myPtrArray[2] = {0, 0};

I get the "expected expression" syntax error. Why?

Note, I'm using g++ and the code above occurs in a class constructor:

template <class T>
    RBTree<T>::RBTree() {
        m_Data = T();
        m_Children = {0, 0};
        m_Parent = 0;
        m_Color = BLACK;
    }

where the class members in question are declared as:

T m_Data;
RBTree<T> * m_Children[2];
RBTree<T> * m_Parent;
bool m_Color;

Upvotes: 0

Views: 679

Answers (2)

yzn-pku
yzn-pku

Reputation: 1082

The form T * myPtrArray[2] = {0, 0}; is called aggregate initialization. It has no counterpart in assignment, so writing

T * myPtrArray[2];
myPtrArray = {0, 0};

is invalid.

In the case of class construction, aggregate initialization is unavailable in c++98/03.

If your compiler supports c++11 standard, you can use uniform initialization syntax. There are two ways to initialize m_Children in your example:

#1

In constructor:

template <class T>
RBTree<T>::RBTree(): m_Children {0, 0} /* other init here */ {

}

#2

During class member declaration:

T m_Data;
RBTree<T> * m_Children[2] {0, 0};
RBTree<T> * m_Parent;
bool m_Color;

Upvotes: 1

Hawkings
Hawkings

Reputation: 533

As of C++11, you can use nullptr instead of 0. Using nullptr is preferred, as it is a pointer instead of an integer. Then, you could do:

T * myPtrArray[2] = {nullptr, nullptr};

Anyway, your code works fine on my compiler, you can see an example using both 0 and nullptr that compiles without errors on ideone.

Upvotes: 0

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