Initializing class member arrays in class constructors?

Question

Here's my header file with the array Data that my teacher wants to initialize in Heap's constructor.

#ifndef HEAP_H
#define HEAP_H

class Heap
{
private:
    int Data [100];
    int Parent(int);
    int RightChild(int);
    int LeftChild(int);
    void Heapify(int*, int);
    void BuildHeap(int*);

public:
    Heap();
    void insert(int*);
    void HeapSort(int*);
    void ExtractMaximum(int*);
    int Maximum(int*);
    void PrintHeap(int*);
    int heapsize;
    int* GetData();
};

#endif

The Constructor is here:

Heap::Heap()
{
    Data = {4, 12, 3, 19, 23, 5, 32, 11, 2, 24}; 
    heapsize = 10;
    BuildHeap(Data); //build a heap with initial values
}

Whenever I run the code with the first line of code in the constructor, initializing the array, I get the following warning:

Warning: extended initializer lists only available with -std=c++0x or -std=gnu++0x

Clearly I'm doing something wrong, and this is the only error/warning I have with this code, and it runs when I take away the line of code initializing Data.

I wouldn't necessarily say you're doing something wrong by using C++11 features, unless your teacher specifically told you not to. — ildjarn
– ildjarn, Commented Nov 10, 2011 at 22:21
Read the warning. It's telling you what compiler option you should use to make this work. Instead of g++ ..., g++ -std=c++0x .... — David Thornley
– David Thornley, Commented Nov 10, 2011 at 22:29

ildjarn · Accepted Answer · 2011-11-14 18:48:34Z

2

If you're limited to using C++03, then I would take this approach:

#include <algorithm>

Heap::Heap()
  : Data() // value-initialize Data so initial elements are 0 instead of random
  , heapsize(10) // initialize here instead of constructor body for consistency
{
    static int const initData[] = { 4, 12, 3, 19, 23, 5, 32, 11, 2, 24 };
    std::copy(initData, initData + sizeof(initData) / sizeof(initData[0]), Data);
    BuildHeap(Data); //build a heap with initial values
}

If you are allowed to use C++11 functionality, then what you have is more or less fine, you just need to actually inform your compiler that you intend to use C++11 functionality (-std=c++0x).

edited Nov 14, 2011 at 18:48

answered Nov 10, 2011 at 22:44

ildjarn

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Comments

Mark Ransom · Accepted Answer · 2011-11-10 22:26:15Z

0

You're trying to assign an initializer list to the variable at a time after it has been created. As noted by the error message, this was not allowed until recent changes to C++ were ratified only a short time ago, probably well after your compiler was created.

It's doubtful that you really want to have a canned bunch of data built into your class. The more usual approach would be to pass the data as parameters into the constructor. The code that creates the object would have an array that is initialized as in your example, and pass that array into the constructor. The constructor would make a copy.

answered Nov 10, 2011 at 22:26

Mark Ransom

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Comments

Werner Henze · Accepted Answer · 2020-05-10 19:03:26Z

0

Take a look here: http://en.wikipedia.org/wiki/C%2B%2B11#Initializer_lists

This is OK, the warning just tells you that you are using a new C++ feature but the compiler was not told so at the command line. The compiler wants you to tell him on the command line (with -std=c++0x) that your code is written along the new C++ standard.

edited May 10, 2020 at 19:03

answered Nov 10, 2011 at 22:18

Werner Henze

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