C++ error initializing array

Question

I want to initialize the array car.places[2][3] but there's always zero in the array. Please can someone tell me what I´m doing wrong, here is the code:

#include <iostream>
#include <string>

using namespace std;

class reserv
{
public:
  int places[2][3];
} car;


int main () {

car.places[2][3] = (
            (1, 2, 3),
            (4, 5, 6)
        );

for(int i=0;i<2;i++)
{
    for(int j=0;j<3;j++)
    {
      cout << i << "," << j << " " << car.places[i][j] << endl;
    }
}

    return 0;
}

I get this warning form the compiler:

>g++ -Wall -pedantic F_car_test.cpp
F_car_test.cpp: In function 'int main()':
F_car_test.cpp:16:11: warning: left operand of comma operator has no effect [
-Wunused-value]
       (1, 2, 3),
           ^
F_car_test.cpp:16:14: warning: right operand of comma operator has no effect
[-Wunused-value]
       (1, 2, 3),
              ^
F_car_test.cpp:17:11: warning: left operand of comma operator has no effect [
-Wunused-value]
       (4, 5, 6)
           ^
F_car_test.cpp:17:14: warning: right operand of comma operator has no effect
[-Wunused-value]
       (4, 5, 6)
              ^

Thanks in advance,

"Theres always zero in the array" What do you mean? You are getting only zero? — SandBag_1996
– SandBag_1996, Commented May 7, 2014 at 18:33
You're not initializing the array, you're assigning to it. You can't assign to arrays. — Barmar
– Barmar, Commented May 7, 2014 at 18:37

Simon · Accepted Answer · 2014-05-07 18:37:29Z

1

You cannot do it after the declaration without a loop.

Here is how to do it in a loop:

for (int i = 0; i < 2; ++i) {
    for (int j = 0; j < 3; ++j) {
        car.places[i][j] = 1 + 3 * i + j;
    }
}

answered May 7, 2014 at 18:37

Simon

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Comments

legends2k · Accepted Answer · 2014-05-07 18:40:34Z

1

You cannot initialize once an object for a struct/class is created; it's called initialization for a reason. Initialize it this way

#include <iostream>

struct reserv
{
  int places[2][3];
} car = {{{1, 2, 3}, {4, 5, 6}}};


int main()
{
  for(int i = 0; i < 2; ++i)
  {
    for(int j = 0; j < 3; ++j)
    {
      std::cout << i << "," << j << " " << car.places[i][j] << std::endl;
    }
  }
}

answered May 7, 2014 at 18:40

legends2k

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Comments

Vlad from Moscow · Accepted Answer · 2014-05-07 18:45:51Z

0

This record

car.places[2][3]

denotes element places[2][3] of data member places of class reserv (or more precisely of object car).

The array was already created as a part of object car that you defined in the global name space.

Write instead

class reserv
{
public:
  int places[2][3];
} car  = { {
            {1, 2, 3},
            {4, 5, 6}
         } };

edited May 7, 2014 at 18:45

answered May 7, 2014 at 18:40

Vlad from Moscow

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Comments

cangrejo · Accepted Answer · 2014-05-07 18:49:36Z

0

In C++, you can only initialize arrays with initializer lists upon declaration. Since in this case your array is a class member, you can (and should) do it in the constructor.

 reserv::reserv():places{{1,2,3},{4,5,6}}{};

You must enable std=c++0x in order to use this.

edited May 7, 2014 at 18:49

answered May 7, 2014 at 18:44

cangrejo

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