C++ 使用指针调整类数组的大小

我的程序中有这段代码。我想创建一个类Ship的数组，它的大小在满的时候会改变。之前我初始化了SIZE=3，Ship*list=newship[SIZE]。当我运行它时，它在我的数组已满后停止工作，这应该执行以下代码：

if(count >= SIZE)
{
    Ship *hold = new Ship[SIZE];       // to hold for a while value of list
    for(int q = 0; q < SIZE; q++)   
        hold[q] = list[q];
    delete[] list;                     //delete list

    Ship *list = new Ship[SIZE + 10];  //set a new size for list
    for(int q = 0; q < SIZE - 10; q++)
        list[q] = hold[q];
    delete[] hold;
}

不需要等待，只需将旧列表复制到新列表即可

但是代码中真正的错误是，你没有改变大小，但你认为它已经改变了

Ship *list = new Ship[SIZE + 10];  //set a new size for list
for(int q = 0; q < SIZE - 10; q++)

应该是

Ship *list = new Ship[SIZE + 10];  //set a new size for list
for(int q = 0; q < SIZE; q++)
   ...
SIZE += 10;

list = new Ship[SIZE + 10];  //set a new size for list

这是您的代码，所有错误都已修复

if(count >= SIZE)
{
    Ship *new_list = new Ship[SIZE + 10];      //make the new list
    for(int q = 0; q < SIZE; q++)              //copy from the old list
        new_list[q] = list[q];
    delete[] list;                             //delete the old list
    list = new_list;                           //use the new list
    SIZE += 10;                                //set a new size for list
}

---

向量稍微容易一点，实际上要容易得多。你应该使用它。

使用指针时要小心

// -------------- include directives:
#include <iostream>
#include <string>

// -------------- your class definitions
class ship {
public:
    ship() {}
    virtual ~ship() {}
};

// ------- declaration state
#define ADDITIONAL_RESERVED_SLOTS (10)
unsigned int arraySize{3};
unsigned int shipCount{}; // initial with zero count
ship* shipArray{nullptr}; // its very important to fill pointers with null for initialialization
void addNewShip(const ship& new_ship); // function prototype

使用如下所示的定义通用函数将新装运添加到阵列中：

void addNewShip(const ship& new_ship) {
    if(++shipCount > arraySize) {
        arraySize += ADDITIONAL_RESERVED_SLOTS;
        // allocate new array
        ship* pNewShipArray = new ship[arraySize];
        // zero allocated memory for pervent from mistakes
        std::memset(pNewShipArray, 0, (sizeof(ship) * arraySize));
        // copy previuse data in to the new array
        std::memcpy(pNewShipArray, shipArray, (sizeof(ship) * (shipCount - 1)));

        // delete previuse array
        delete[] shipArray;

        // now you can use shipArray
        shipArray = pNewShipArray;

    }
    // add new ship in to your array
    shipArray[shipCount - 1] = new_ship; // be carefull!! if you have pointers in your ship class you most handle them too.
}

---

你有没有考虑过？向量是一种方法，但是如果你-删除[]列表；将其复制到新阵列后，只需要一个复制循环。例：船*舱=新船[尺寸]；forint q=0；首先读取一个名为list的东西，然后创建一个新的list变量，该变量不是您从中读取的列表，并填充它。新列表从范围中退出，这意味着您将永远无法再使用它。std:：vector-将解决所有这些问题。你为什么不用它？std:：vector的全部目的是使数组具有可调整大小的功能。它起作用了，但只是想知道，list=new\u list意味着list将与new\u list共享相同的内存位置，对吗？这就是我以后不需要删除新列表的原因吗？正是这个原因。因为list和new_list在list=new_list之后指向同一内存，如果删除了new_list，则将无法再使用list。回答问题时，请尝试在代码之前添加一些解释。

// -------------- include directives:
#include <iostream>
#include <string>

// -------------- your class definitions
class ship {
public:
    ship() {}
    virtual ~ship() {}
};

// ------- declaration state
#define ADDITIONAL_RESERVED_SLOTS (10)
unsigned int arraySize{3};
unsigned int shipCount{}; // initial with zero count
ship* shipArray{nullptr}; // its very important to fill pointers with null for initialialization
void addNewShip(const ship& new_ship); // function prototype

// ------- allocate array dynamicly with  3 slot
ship* shipArray = new ship[arraySize];
// zero allocated memory for pervent from mistakes
std::memset(shipArray, 0, (sizeof(ship) * arraySize));

void addNewShip(const ship& new_ship) {
    if(++shipCount > arraySize) {
        arraySize += ADDITIONAL_RESERVED_SLOTS;
        // allocate new array
        ship* pNewShipArray = new ship[arraySize];
        // zero allocated memory for pervent from mistakes
        std::memset(pNewShipArray, 0, (sizeof(ship) * arraySize));
        // copy previuse data in to the new array
        std::memcpy(pNewShipArray, shipArray, (sizeof(ship) * (shipCount - 1)));

        // delete previuse array
        delete[] shipArray;

        // now you can use shipArray
        shipArray = pNewShipArray;

    }
    // add new ship in to your array
    shipArray[shipCount - 1] = new_ship; // be carefull!! if you have pointers in your ship class you most handle them too.
}