初始化变量大小的数组类中 [英] initializing array of variable size inside a class

问题描述

我想初始化大小的数组N系从我的构造函数的输入参数。
这工作：

I am trying to initialize an array of size n based off the input argument of my constructor. This works:

//Inside Header
class runningAverage{
    private:
        byte n;
        float array[10];
    public:
        runningAverage(byte);
};

//Inside .cpp
runningAverage::runningAverage(byte a){
    n = a;
    for (byte i = 0; i<n; i++) {
        array[i] = 0;
    }
}

和这不起作用：

//Inside Header
class runningAverage{
    private:
        byte n;
        float array[];
    public:
        runningAverage(byte);
};

//Inside .cpp
runningAverage::runningAverage(byte a){
    n = a;
    for (byte i = 0; i<n; i++) {
        array[i] = 0;
    }
}

我要初始化数组，这样由n指定的大小。这样，我不要随意指定float数组[256]或类似的东西浪费内存。任何帮助AP preciated！

I want to initialize the array so that is the size specified by n. This way I don't waste memory by arbitrarily specifying float array[256] or something like that. Any help is appreciated!

推荐答案

您有实际分配数组;你会想用一个指针类型， int数组[] 是不是你想在那里。由于juanchopanza提醒我们，你也想要么禁止拷贝构造函数和赋值运算符，或实现那些做一个适当的深层复制。

You have to actually allocate the array; and you'll want to use a pointer type, float array[] is not what you think there. As juanchopanza reminds us, you'll also want to either disable the copy constructor and assignment operator, or implement ones that do a proper deep copy.

//Inside Header
class runningAverage{
    private:
        byte n;
        float *array; // <= correct type
    public:
        runningAverage(byte);
        ~runningAverage(); // <= you'll need a destructor to cleanup
    private:
        runningAverage(const runningAverage &);
        runningAverage & operator = (const runningAverage &);
};

//Inside .cpp
runningAverage::runningAverage(byte a){
    array = new float[n]; // <= allocate array
    n = a;
    for (byte i = 0; i<n; i++) {
        array[i] = 0;
    }
}

// clean up
runningAverage::~runningAverage(){
    delete[] array;
}

不过，如果您在您的处置有一些动态的，全自动的容器（如的std ::矢量），你可能想使用代替 - 那么你不必对付拷贝/转让/析构函数/内存管理。

However, if you have some dynamic, automatic container at your disposal (e.g. std::vector) you might want to use that instead - then you don't have to deal with copy / assignment / destructor / memory management.

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