Shopping_list::Shopping_list(const Shopping_list & m)//拷贝构造函数,实现“深拷贝” {//在此补充本段代码,实现“深拷贝” }
时间: 2023-12-21 14:04:08 浏览: 27
在拷贝构造函数中实现深拷贝,需要对指针类型的成员变量进行新的内存分配,并将原对象的数据复制到新的内存中,而不是简单地复制指针地址。
例如,如果有一个指向动态分配内存的指针成员变量 data,可以这样实现深拷贝:
```c++
Shopping_list::Shopping_list(const Shopping_list & m) {
// 分配新的内存
data = new int[m.size];
size = m.size;
// 复制数据
for (int i = 0; i < size; ++i) {
data[i] = m.data[i];
}
}
```
注意,拷贝构造函数不应当修改原对象的数据,因此应该使用 const 引用作为参数。同时,如果对象的成员变量包含了其他动态分配内存的对象,也需要在拷贝构造函数中递归地调用它们的拷贝构造函数来实现深拷贝。
相关问题
private: Goods *gs; //用于建立堆区数组,存放商品信息 int nums; //堆区数组中的元素个数(商品种类数) float value;//购物所需总金额 Shopping_list::Shopping_list(const Shopping_list & m)//拷贝构造函数,实现“深拷贝” {//在此补充本段代码,实现“深拷贝” }
假设 `Goods` 类已经实现了拷贝构造函数,可以这样实现 `Shopping_list` 的深拷贝:
```c++
Shopping_list::Shopping_list(const Shopping_list & m) {
nums = m.nums;
value = m.value;
if (nums > 0) {
// 分配新的内存
gs = new Goods[nums];
// 复制数据
for (int i = 0; i < nums; ++i) {
gs[i] = m.gs[i]; // 调用 Goods 的拷贝构造函数
}
} else {
gs = nullptr;
}
}
```
注意,这里需要先复制 `nums` 和 `value` 两个基本类型成员变量,然后对指针成员变量 `gs` 进行深拷贝。同时,为了避免对空指针进行解引用等操作,需要在构造函数中对 `gs` 进行初始化为 `nullptr`。
Imagine you are writing a program to manage a shopping list. Using a vector to hold the shopping list items, write a print function to print out the contents of a vector of strings. Test your print function with a main program that does the following: Create an empty vector. Print it. Append the items, "eggs," "milk," "sugar," "chocolate," and "flour" to the list. Print it. Remove the last element from the vector. Print it. Append the item, "coffee" to the vector. Print it. Write a loop that searches for the item, "sugar" and replace it with "honey." Print the vector. Write a loop that searches for the item, "milk," and then remove it from the vector. Print the vector. Search for the item, "chocolate," and insert the item "tea" before it. Print the vector one more time.
Here is a possible implementation of the program:
```c++
#include <iostream>
#include <vector>
#include <algorithm> // for std::replace
void print_vector(const std::vector<std::string>& v) {
std::cout << "[";
for (size_t i = 0; i < v.size(); ++i) {
std::cout << v[i];
if (i < v.size() - 1) {
std::cout << ", ";
}
}
std::cout << "]" << std::endl;
}
int main() {
std::vector<std::string> shopping_list;
std::cout << "Empty list: ";
print_vector(shopping_list);
shopping_list.push_back("eggs");
shopping_list.push_back("milk");
shopping_list.push_back("sugar");
shopping_list.push_back("chocolate");
shopping_list.push_back("flour");
std::cout << "Initial list: ";
print_vector(shopping_list);
shopping_list.pop_back();
std::cout << "List after removing last item: ";
print_vector(shopping_list);
shopping_list.push_back("coffee");
std::cout << "List after adding coffee: ";
print_vector(shopping_list);
for (auto& item : shopping_list) {
if (item == "sugar") {
item = "honey";
}
}
std::cout << "List after replacing sugar with honey: ";
print_vector(shopping_list);
shopping_list.erase(std::remove(shopping_list.begin(), shopping_list.end(), "milk"), shopping_list.end());
std::cout << "List after removing milk: ";
print_vector(shopping_list);
auto it = std::find(shopping_list.begin(), shopping_list.end(), "chocolate");
if (it != shopping_list.end()) {
shopping_list.insert(it, "tea");
}
std::cout << "List after inserting tea before chocolate: ";
print_vector(shopping_list);
return 0;
}
```
The `print_vector` function takes a reference to a const vector of strings and prints its contents between square brackets, separated by commas and spaces, followed by a newline.
The `main` function creates an empty vector of strings called `shopping_list`, prints it using `print_vector`, appends the items using `push_back`, prints the list again, removes the last item using `pop_back`, prints the list again, appends "coffee", prints the list again, replaces "sugar" with "honey" using a range-based for loop and `std::replace`, prints the list again, removes "milk" using `std::find` and `std::erase`, prints the list again, inserts "tea" before "chocolate" using `std::find` and `std::insert`, and prints the list one last time.
The output of the program should be:
```
Empty list: []
Initial list: [eggs, milk, sugar, chocolate, flour]
List after removing last item: [eggs, milk, sugar, chocolate]
List after adding coffee: [eggs, milk, sugar, chocolate, coffee]
List after replacing sugar with honey: [eggs, milk, honey, chocolate, coffee]
List after removing milk: [eggs, honey, chocolate, coffee]
List after inserting tea before chocolate: [eggs, honey, tea, chocolate, coffee]
```