how to set a int array inside a struct in c++

Question

I have

struct board{
    int x[3];
    int y[3];
};

// in the class PatternReader
board PatternReader::testPattern1DX() {
   struct board aBoard;
   int x[3] = { 1,1,1 };
   aBoard = x;
   return aBoard;
}

Error is "incompatible types in assignment of int *".

How do you set arrays that are inside a struct?

You can't assign raw arrays. Use std::array<int, 3> instead. — Borgleader
– Borgleader, Commented Feb 5, 2014 at 19:26
Or if you can't use C++11 or Boost then std::copy should do the trick. — Captain Obvlious
– Captain Obvlious, Commented Feb 5, 2014 at 19:26

David Heffernan · Accepted Answer · 2014-02-05 19:27:35Z

4

You cannot assign arrays. However, you can can initialize the struct:

board PatternReader::testPattern1DX() 
{
   board aBoard = { 
       {1, 1, 1}, 
       {2, 2, 2} 
   };
   return aBoard;
}

This initializes y as well as x.

answered Feb 5, 2014 at 19:27

David Heffernan

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3 Comments

Vlad from Moscow Over a year ago

@TheOn It is valid code for C++ 2003 because board is an aggregate.

Creris Over a year ago

hmm..I should do research next time lol, thanks for correcting me, comment removed

bames53 Over a year ago

Directly initializing the variable, rather than initializing a separate variable and then performing an assignment, is the right thing to do. However it is also a good idea to avoid raw arrays and to use std::array instead. This answer still works after replacing the raw arrays with std::array.

Lother · Accepted Answer · 2014-02-05 20:04:51Z

1

Add an initializer function to the board struct:

struct board
{
   int x[3];
   int y[3];

   void initX(int* values)
   {
      for(int i = 0; i < 3; i++)
         x[i] = values[i]
   }
};

Then use it:

board PatternReader::testPattern1DX() 
{
   struct board aBoard;
   int x[3] = { 1,1,1 };
   aBoard.initX(x);
   return aBoard;
}

answered Feb 5, 2014 at 20:04

Lother

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Comments

Community · Accepted Answer · 2017-05-23 11:56:06Z

0

Your code

int x[3] = { 1,1,1 };
aBoard = x;

is creating a variable of type int* with the initial values 1,1,1. You are then trying to assign that to a variable of type board. You don't want to do that. I think you intended:

int x[3] = { 1,1,1 };
aBoard.x = x;

Note the .x at the end of aBoard. However, this is still wrong. You can't assign arrays like that. Look up "copying arrays" instead. Is there a function to copy an array in C/C++?

Honestly, I would suggest making board a class with constructors and and then you can make the constructors behave as you want, and also look into overloading assignment operators. But for now, trying copying from x to aBoard.x is probably what you want.

edited May 23, 2017 at 11:56

CommunityBot

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answered Feb 5, 2014 at 19:45

m24p

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2 Comments

bames53 Over a year ago

"is creating a variable of type int*" No, arrays and pointers are not the same. The variable is in fact an array and its type is 'array of 3 ints'. If it were really a pointer then this would be legal: int x[3] = {1,1,1}; x = nullptr;

m24p Over a year ago

Thank you for making sure the technical stuff is accurate. Yes, arrays and pointers are not exactly the same. I used the term "int*" because in the code aBoard = x; it tries to assign aBoard to the int* from x, thus the error: "incompatible types in assignment of int *"

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