I have a basic C++ class .The header looks like this:
#pragma once
class DataContainer
{
public:
DataContainer(void);
~DataContainer(void);
int* getAgeGroup(void);
int _ageGroupArray[5];
private:
int _ageIndex;
};
Now inside the cpp file of the class I want to intialize the _ageGroupArray[5] with default values inside the class contructor like this:
#include "DataContainer.h"
DataContainer::DataContainer(void)
{
_ageGroupArray={20,32,56,43,72};
_ageIndex=10;
}
int* DataContainer::getAgeGroup(void){
return _ageGroupArray;
}
DataContainer::~DataContainer(void)
{
}
Doing it I am getting "Expression must be a modifiable lvalue" on _ageGroupArray line.So is it entirely impossible to initialize an array object in the constructor? The only solution I found was to define the array outside scope identifiers .Any clarification on this will be greatly appreciated.
In the current standard, as you have already noticed, you cannot initialize a member array in the constructor with the initializer list syntax. There are some workarounds, but none of them is really pretty:
// define as a (private) static const in the class
const int DataContainer::_age_array_size = 5;
DataContainer::DataContainer() : _ageIndex(10) {
int tmp[_age_array_size] = {20,32,56,43,72};
std::copy( tmp, tmp+_age_array_size, _ageGroupArray );
}
If the values in the array are always the same (for all object in the class) then you can create a single static copy of it:
class DataContainer {
static const int _ageGroupArraySize = 5;
static const int _ageGroupArray[ _ageGroupArraySize ];
// ...
};
// Inside the cpp file:
const int DataContainer::_ageGroupArray[_ageGroupArraySize] = {20,32,56,43,72};
You can Initialize a array when you Create/Declare it, not after that.
You can do it this way in constructor :
_ageGroupArray[0]=20;
_ageGroupArray[1]=32;
_ageGroupArray[2]=56;
_ageGroupArray[3]=43;
_ageGroupArray[4]=72;
It is important to know that this is Assignment & not Initialization.
try this:
int ageDefault[]={20,32,56,43,72};
memcpy(_ageGroupArray, ageDefault, sizeof(ageDefault));