C++私有成员函数

时间：03-07来源：作者：点击数：34

到目前为止，我们所看到的所有类成员函数都是公共函数，这意味着它们可以通过类外部的程序代码调用。但是，类也经常需要一些函数来进行内部处理，这样的函数不应该由类外的代码调用，它们应该被声明为私有。

下面的程序显示了具有私有函数的类的示例。SimpleStat 类被设计用于从发送给它的一组非负整数中查找和报告信息，如平均值和最大数字。但是，一旦某个数字已经被接收并被添加到累计汇总，那么它将不被保留，所以该类不能等以后再确定哪个数字是最大的，它必须通过检查其读取的每个数字来查看它是否大于之前读取的任何数字。isNewLargest 私有函数正是执行此操作的。

#include <iostream>
using namespace std;
class SimpleStat
{
    private:
        int largest;    // The largest number received so far
        int sum;    // The sum of the numbers received
        int count;    // How many numbers have been received
        bool isNewLargest(int); // This is a private class function

    public:
        SimpleStat();    // Default constructor
        bool addNumber(int);
        double getAverage();
   
    int getLargest()
    {
        return largest;
    }
    int getCount()
    {
        return count;
    }
};
SimpleStat::SimpleStat()
{
    largest = sum = count = 0;
}

bool SimpleStat::addNumber(int    num)
{
    bool goodNum = true;
    if (num >= 0)    // If num is valid
    {
        sum += num;    // Add it to the sum
        count++;    // Count it
        if(isNewLargest(num))    // Find out if it is
        largest = num;    // the new largest
    }
    else    //num is invalid
        goodNum = false;
    return goodNum;
}
bool SimpleStat::isNewLargest(int num)
{
    if (num > largest)
        return true;
    else
        return false;
}
double SimpleStat::getAverage()
{
    if (count > 0)
        return static_cast<double>(sum) / count;
    else
        return 0;
}
//Client Program
int main()
{
    int num;
    SimpleStat statHelper;

    cin >> num;
    while (num >= 0)
    {
        statHelper.addNumber(num);
        cin >> num;
    }
    cout << "\nYou entered "<< statHelper.getCount() << " values. \n";
    cout << "The largest value was " << statHelper.getLargest () << endl;
    cout << "The average value was " << statHelper.getAverage () << endl;
    return 0;
}