How to access variable from included Header file in cpp?

Question

Hi Its my first time creating header file and accessing its variables in cpp. I have 2 files arrayyy.h and array.cpp and their code is mentioned below.

arrayyy.h

#ifndef ARRAYYY_H_
#define ARRAYYY_H_

namespace a {

class arrayyy {
public:
    arrayyy();
    virtual ~arrayyy();
private:
    const static int num = 4;
    int* arr = new int[num];
};

} /* namespace a */

#endif /* ARRAYYY_H_ */

arrayyy.cpp

#include "arrayyy.h"
#include "iostream"
using namespace std;

namespace a {

arrayyy::arrayyy() {


    cout << a::arrayyy::num ;

    a::arrayyy::arr = {8,2,9,4};

    for(int i =0; i < a::arrayyy::num; i++)
    {
        cout << arr;
    }
}

arrayyy::~arrayyy() {

}
//int main ()
//{
//  cout << a::arrayyy::num ;
//}

} /* namespace a */

Instead of getting output CTD build console is showing following warnings

12:28:10 **** Incremental Build of configuration Debug for project TRiES ****
make all 
Building file: ../src/arrayyy.cpp
Invoking: Cross G++ Compiler
g++ -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"src/arrayyy.d" -MT"src/arrayyy.o" -o "src/arrayyy.o" "../src/arrayyy.cpp"
In file included from ../src/arrayyy.cpp:8:0:
../src/arrayyy.h:19:24: warning: non-static data member initializers only available with -std=c++11 or -std=gnu++11
  int* arr = new int[num];
                        ^
../src/arrayyy.cpp: In constructor ‘a::arrayyy::arrayyy()’:
../src/arrayyy.cpp:19:28: warning: extended initializer lists only available with -std=c++11 or -std=gnu++11
  a::arrayyy::arr = {8,2,9,4};
                            ^
../src/arrayyy.cpp:19:18: error: cannot convert ‘<brace-enclosed initializer list>’ to ‘int*’ in assignment
  a::arrayyy::arr = {8,2,9,4};
                  ^
src/subdir.mk:18: recipe for target 'src/arrayyy.o' failed
make: *** [src/arrayyy.o] Error 1

12:28:10 Build Finished (took 417ms)

I've checked already asked questions but their answers are not helping me in this regard. I've used extern as well. Being a beginner I need guidance in this scenario. Please guide me to remove the warnings. Thank you.

1. You need to initialise `num` in the constructor. 2. Arrays require a size *constant* already at compile time (i. e. `arr[num]` is simply not possible, at least not the way you try). — Aconcagua, Apr 18 '18 at 07:20
Possible duplicate of [Array\[n\] vs Array\[10\] - Initializing array with variable vs real number](https://stackoverflow.com/questions/15013077/arrayn-vs-array10-initializing-array-with-variable-vs-real-number). The compiler is telling you what is wrong. You cannot use a `non static variable` for an array size. — user1810087, Apr 18 '18 at 07:22
@user1810087 Static alone is not sufficient, must be const, too... — Aconcagua, Apr 18 '18 at 07:26
Thank you all for suggestions. Can you please point out what else am i doing wrong? — Farwa Ansari, Apr 18 '18 at 07:44
There is no need to use `a::arrayyy::arr`if you are inside your class and inside your namespace. Just `arr`should be work fine. — haggi krey, Apr 18 '18 at 07:50
Please start class names with a capital letter, e.g. Arrayyy in your case. — YesThatIsMyName, Apr 18 '18 at 07:55

score 1 · Accepted Answer · edited Jun 20 '20 at 09:12

You have two problems here. The first one is already solved by the compiler:

../src/arrayyy.h:19:24: warning: non-static data member initializers only available with -std=c++11 or -std=gnu++11
int* arr = new int[num];

This feature was added to the language in the C++11 standard. So, to be able to initialize class members in the class declaration, you need to add the option -std=c++11 to the compile options.

The other part is about this line:

a::arrayyy::arr = {8,2,9,4};

This is not something you can do in C++. The member arr is a pointer to some ints. There is no easy way to assign a whole bunch of those ints in one statement. You will have to do this separately:

arr[0] = 8;
arr[1] = 2;
arr[2] = 9;
arr[3] = 4;

You don't have to use the fully qualified name inside the class members. The compiler still understands that you mean the member variable.

How to access variable from included Header file in cpp?

1 Answers1