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,

• SandBag_1996: "Theres always zero in the array" What do you mean? You are getting only zero?
• SandBag_1996: Never mind! I read it wrong..
• Barmar: You're not initializing the array, you're assigning to it. You can't assign to arrays.

Answer 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;
 }
}

Answer 2

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;
 }
 }
}

Answer 3

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}
 } };

Answer 4

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.