c++ - 如何使用带有指针的数组？

Question

我是编程新手，尝试创建一个包含一系列记录的数组，然后让程序接受输入并最终打印出列表的内容。

我在addRecord()函数中记录某些变量的值时遇到问题，因为以下代码的输出如下:

constructor called
-1:-1 Eat lunch

-1:-1 Watch TV

destructor called

为什么我完全错过了对 L1.addRecord(5, 30, "Make dinner");的调用，为什么时间没有过去(它们在构造函数中设置为-1)？

谢谢

#include <iostream>
#include <string>
using namespace std;

class Record {
private:
    int hour;
    int minute;
    string todo;

public:
    Record()
    {
        hour = -1;
        minute = -1;
        todo = "N/A";
    }

    void setData(int hour, int minute, const char* td);
    void setData(Record& e);
    void printRecord();
};

class List
{
private:
    Record* recordArr;
    int maxRecords;
    int actualRecordCount;

public:
    List(int maxRecords);

    List(List& s) {
        actualRecordCount = s.actualRecordCount;
        maxRecords = s.maxRecords;
        recordArr = new Record[maxRecords];
        for (int i = 0; i < actualRecordCount; i++)
        {
            recordArr[i].setData(s.recordArr[i]);
        }

        std::cout << "copy constructor called." << std::endl;
    }
    ~List();
    bool addRecord(int hour, int minute, const char* todo);
    void printList();
};


///////////////////////////

void Record::setData(int hour, int minute, const char* td)
{
    hour = hour;
    minute = minute;
    todo = td;
}

void Record::setData(Record& e) 
{
    hour = e.hour; 
    minute = e.minute;
    todo = e.todo;
}

void Record::printRecord()
{
    std::cout << hour << ":" << minute << " " << todo << std::endl;
}

List::List(int maxRecords)
    : maxRecords(maxRecords)
{
    actualRecordCount = 0;
    recordArr = new  Record[maxRecords];
    std::cout << "constructor called" << std::endl;
}

List::~List()
{
    std::cout << "\ndestructor called";
    delete[] recordArr;
}

bool List::addRecord(int hour, int minute, const char* todo)
{
    Record newRecord; // create new Record
    newRecord.setData(hour, minute, todo); //assign values

    if (actualRecordCount >= maxRecords) // array full
    {
        return false;
    }

    else
    {
        recordArr[actualRecordCount] = newRecord; // put new Record into the array of Entry
        actualRecordCount++; // increment Entry count
        return true;
     }

}

void List::printList()
{
    for (int i = 0; i < actualRecordCount; i++)
    {
        recordArr[i].printRecord();
        cout << endl;
        i++;
    }

}

int main() {

    List L1(20);
    L1.addRecord(2, 30, "Eat lunch");
    L1.addRecord(5, 30, "Make dinner");
  L1.addRecord(7, 30, "Watch TV");
    L1.printList();

}

Answer 1

void Record::setData(int hour, int minute, const char* td)
{
    hour = hour;

“hour”是此 setData()方法的参数名称。因此， hour=hour;将此参数设置为其自身。无论如何，这绝对不会完成任何事情。接下来的其他两个作业也一样。

您的明显意图是初始化碰巧具有相同名称成员的类。当不同的事物在C++中具有相同的名称时，会有一组复杂的规则来选择名称代表的“事物”。这些规则在 =运算符的左侧和右侧相同，因此，这两个 hour最终都引用同一对象:此类方法的参数。

您可以简单地将参数重命名为方法:

void Record::setData(int hourArg, int minuteArg, const char* tdArg)
{
    hour = hourArg;

等等。或者，如果您希望保持参数名称相同，则使内容更明确:

this->hour=hour;