C++ 创建对象的动态数组？

Posted 2023-02-21

【中文标题】C++ 创建对象的动态数组？

【英文标题】：C++ creating dynamic array of objects?

【发布时间】：2014-10-22 23:34:48

【问题描述】：

#include "resistor.h"


void main() 
    srand(GetTickCount()); // Lewt's start by seeding the random number generator so that different runs of our program will always yield fifferent results
    Resistor * pResistor; // Pointer to a resistor class
    int numberOfResistors = 0;  // Variable will hold the user choice of the number of resistors to be created
    cout << "How many resistors do you want to create?" << endl;  // prompt user
    cin >> numberOfResistors;  // Allow the user to enter the number of resistors to be created
    pResistor = new Resistor[numberOfResistors];  // Create an array of objects of class resistor and assign its address to our pointer

    // You will notice that there is a logic error here. All the resistors will have the same value. This
    // is because they were all created at once. To address this issue we need to create each object
    // of the class resistor separately. This means using a loop. This will be up  to you to do
    // It should be a very easy fix
    for (int i = 0; i< numberOfResistors; i++)   // This loop will be used to display the resistor values
        cout << "Resistor # " << i + 1 << " has a value of " << pResistor->getResistance() << " " << (char)234 << endl;  // Display value of resistor pointed to by pResistor
    

    cout << "So far, we have created " << pResistor->getNumerOfResistors() << " resistor(s)" << endl; // Display total number of resistors
    delete[] pResistor; // Delete the array that was created and release the memory that was allocated.
  // end of main

我正在使用此代码进行课堂作业。正如您可能在 cmets 中看到的那样，我的教练在那里输入了一个逻辑错误，我需要修复它。我尝试将 pResistor = new Resistor[numberOfResistors]; 行放在一个 for 循环中，该循环运行用户输入指定的次数（而不是创建一个数组）。问题仍然是每个对象仍然使用相同的值创建 ResistorObject.resistance

任何意见将不胜感激

编辑：下面的代码是我上面试图解释的：

for (int i = 0; i < numberOfResistors; i++) 
    pResistor = new Resistor[i];  // Create an array of objects of class resistor and assign its address to our pointer

然而，当我收到错误时，这将无法编译：

错误 C4703：使用了可能未初始化的局部指针变量“pResistor”

【问题讨论】：

如何设置阻力？它是否在用户定义的（非默认）构造函数中指定？你应该使用 RNG 这样做吗？

你不需要注释每一行代码——我们知道 C++。过度注释实际上会使您的代码更难阅读。

向量是显而易见的方法，例如 user3670482 的答案显示。该向量包含许多指向不同电阻器的单独指针，每个电阻器都被分配，因此可以不同地设置它们的电阻，但是你又如何设置电阻？另外，你应该在没有向量的情况下这样做吗？

将 pResistor->getResistance() 更改为 pResistor[i].getRsistance() 。不要更改您的new

您的编辑是内存泄漏中心：它不断尝试将不同数量的内存分配给同一个指针变量，而您却无法再次释放它。您的代码正在尝试为 pResistor 分配 0 个电阻，然后是 1，然后是 2，然后是 3……等等。

【参考方案1】：

srand(GetTickCount());
Resistor * pResistor = NULL; 
vector<Resistor*> resList;
int numberOfResistors = 50; // Use your cin cout here
for (size_t i = 0; i < numberOfResistors; i++)

    pResistor = new Resistor;
    // Assuming some sort of pResistor->SetResistance( /* val */ )
    resList.push_back(pResistor);


for (int i = 0; i< numberOfResistors; i++)   // This loop will be used to display the resistor values
    cout << "Resistor # " << i + 1 << " has a value of " << resList[i]->getResistance() << " " << (char)234 << endl;  // Display value of resistor pointed to by pResistor


cout << "number of resistors : " << resList.size() << endl;

每个电阻都需要自己的参考，所有参考都必须添加到有序列表中。 std::vector 用于制作有序列表