C++数据结构第20课、数组类的创建（下）

课程目标 — 完成 DynamicArray 类的具体实现 DynamicArray 设计要点 — 类模板 　　动态确定内部数组空间的大小 　　实现函数返回数组长度 　　拷贝构造和赋值操作DynamicArray 类的声明

DynamicArray.h

#ifndef DYNAMICARRAY_H #define DYNAMICARRAY_H #include "Array.h" namespace DTLib { template<typename T> class DynamicArray : public Array<T> { protected: int m_length; public: DynamicArray(int length) { this->m_array = new T[length]; if(this->m_array != nullptr) { this->m_length = length; } else { THROW_EXCEPTION(NoEnoughMemoryException, "no memory to creat DynamicArray Object..."); } } DynamicArray(const DynamicArray<T>& obj) { this->m_array = new T[obj.m_length]; if(this->m_array != nullptr) { for(int i = 0; i < obj.m_length; i++) { this->m_array[i] = obj.m_array[i]; } this->m_length = obj.m_length; } else { THROW_EXCEPTION(NoEnoughMemoryException, "no memory to copy the Object..."); } } DynamicArray<T>& operator=(const DynamicArray<T>& obj) { if(this != &obj) { T* array = new T[obj.m_length]; if(array != nullptr) { for(int i = 0; i < obj.m_length; i++) { array[i] = obj.m_array[i]; } T* temp = this->m_array; this->m_array = array; this->m_length = obj.m_length; delete []temp; } else { THROW_EXCEPTION(NoEnoughMemoryException, "no memory to copy the Object..."); } } return *this; } void resize(int length) { if(this->m_length != length) { T* array = new T[length]; if(array != nullptr) { int len = (this->m_length < length ? this->m_length : length); for(int i = 0; i < len; i++) { array[i] = this->m_array[i]; } T* temp = this->m_array; this->m_array = array; this->m_length = length; delete[] temp; } else { THROW_EXCEPTION(NoEnoughMemoryException, "no memory to resize the Object..."); } } } int length()const { return m_length; } ~DynamicArray() { delete []this->m_array; } }; } #endif // DYNAMICARRAY_H

main.cpp

#include <iostream> #include "StaticArray.h" #include "DynamicArray.h" using namespace std; using namespace DTLib; int main() { DynamicArray<int> s1(5); for(int i = 0; i < s1.length(); i++) { s1[i] = i * i; } for(int i = 0; i < s1.length(); i++) { cout << s1[i] << endl; } cout << endl; DynamicArray<int> s2(10); s2 = s1; s2.resize(3); for(int i = 0; i < s2.length(); i++) { cout << s2[i] << endl; } s2[4] = 100; return 0; }

问题 DynamicArray 类中的函数实现存在重复的逻辑，如何进行代码优化？重复代码逻辑的抽象 — init 　　对象构造时的初始化操作 　　 — copy 　　在堆空间中申请新的内存，并执行拷贝操作 　　 — update 　　将指定的堆空间作为内部存储数组使用 #ifndef DYNAMICARRAY_H #define DYNAMICARRAY_H #include "Exception.h" #include "Array.h" namespace DTLib { template <typename T> class DynamicArray : public Array<T> { protected: int m_length; T* copy(T* array, int len, int new_len) //把本来有的空间赋值给新申请的空间 { T* ret = new T[new_len]; if(ret != nullptr) { int size = (len < new_len ? len : new_len); for(int i = 0; i < size; i++) { ret[i] = array[i]; } } return ret; } void update(T* array, int length) { if(array != nullptr) { T* temp = this->m_array; this->m_array = array; this->m_length = length; delete []temp; } else { THROW_EXCEPTION(NoEnoughMemoryException, "No memory to update the Object"); } } void init(T* array, int length) { if(array != nullptr) { this->m_array = array; this->m_length = length; } else { THROW_EXCEPTION(NoEnoughMemoryException, "No memory to init the Object"); } } public: DynamicArray(int length) { init(new T[length], length); } DynamicArray(const DynamicArray<T>& obj) { init(copy(obj.m_array, obj.m_length, obj.m_length), obj.m_length); } DynamicArray<T>& operator=(const DynamicArray<T>& obj) { if(this != &obj) { update(copy(obj.m_array, obj.m_length, obj.m_length), obj.m_length); } return *this; } void resize(int length) { if(this->m_length != length) { update(copy(this->m_array, m_length, length), length); } } int length()const { return m_length; } ~DynamicArray() { delete [](this->m_array); } }; } #endif // DYNAMICARRAY_H

小结：

StaticArray 通过封装原生数组的方式实现数组类DynamicArray 动态申请堆空间，使得数组长度动态可变数组对象能够代替原生数组，并且使用上更安全代码优化是项目开发过程中不可或缺的环节