在C Intitialzing数组++类，并修改的左值问题 [英] Intitialzing an array in a C++ class and modifiable lvalue problem

问题描述

我有一个基本的C ++类.The头看起来是这样的：

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;

};

现在的类cpp文件里面我想用类构造像这里面的默认值，并初始化的_ageGroupArray [5]：

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)
{
}

做这件事我收到的Ex pression必须修改的左值关于_ageGroupArray line.So是完全不可能初始化在构造一个数组对象？我发现的唯一的解决办法是定义范围之外的标识符阵列。任何澄清，这将是极大的AP preciated。

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.

推荐答案

在当前的标准，因为你已经注意到了，你无法​​初始化与初始化列表的语法构造一个成员数组。有一些解决方法，但没有人真的是pretty：

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 ); 
}

如果数组中的值总是相同（类中的所有对象），那么你可以创建一个单一的静态副本：

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};

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