最近学习了数据结构，对线性表有了比较深刻的认识，并和c++中容器的实现对照了下，有了点小收获，记录下来。。
1，首先线性表有2种存储结构：顺序存储结构，链式存储结构。（先说顺序存储，之后看链表list的时候再说）顺序存储就相当于数组，连续的存储地址，插入和删除要移动大量的数据元素，因为地址是连续的，但是随机访问能力好，也就是下标访问元素的能力。
2.对c++中vector类模板的实现，改变了数组固定大小的缺点，可以动态添加或删除元素改变容器的大小，有很多的函数成员，使用起来也很方便。
其实vector就是可变大小的数组，支持快速随机访问，除了尾部之外的地方插入和删除元素很慢。（因为要保持连续的线性存储空间）
3.自己写了一个vector类模板，只是实现了部分功能，一般的大小，插入，删除，访问等。。看了primer之后利用allocator类实现了另一个版本。
4.代码如下Vector.h为头文件。
/*vector是可变大小的数组，是顺序存储结构，支持快速的随机访问，在尾部之外的位置插入和删除元素很慢*/ #ifndef VECTOR_H #define VECTOR_H #include<cassert> #include<iostream> using namespace std; template<typename T> class Vector { public: enum{ SPARE_CAPACITY = 5 }; typedef T* iterator; typedef const T* const_iterator; //构造函数 explicit Vector(int initsize = 0); //explicit是为了防止让一个实参的构造函数发生隐式转换 Vector(int initsize, T value); Vector(iterator b, iterator e); //接受两个迭代器创建拷贝的构造函数 ,这里的迭代器的创建是指针，见上面 Vector(std::initializer_list<T> l); Vector(const Vector &rhs); Vector<T>& operator=(const Vector & rhs); ~Vector() { delete[] elem;} //常量成员函数，不改变类的成员,this指针为指向常量的常量指针，因为常量对象不能调用非常量数据成员，而非常量对象都可以调用 bool empty()const { return thesize == 0;} int size() const {return thesize;} int capacity() const { return thecapacity; } iterator begin() {return &elem[0];} iterator end() {return &elem[thesize];} const_iterator cbegin()const {return &elem[0];} const_iterator cend() const {return &elem[thesize];} bool operator==(const Vector<T>& rhs); bool operator!=(const Vector<T>& rhs); void reserve(int newcapacity); void resize(int newsize, const T &thevalue); void resize(int newsize); void shrink_to_fit(); T &operator[](int index); const T &operator[](int index) const; T &front(); const T &front() const; T &back(); const T &back() const; void push_back(const T &x); iterator insert(iterator b, const T &value); void pop_back() {thesize--;} iterator erase(iterator b); void clear(); private: T *elem; int thesize; int thecapacity; }; /******************************************构造函数******************************************/ template <typename T> Vector<T>::Vector(int initsize = 0) :thesize(initsize), thecapacity(initsize + SPARE_CAPACITY) { elem = new T[thecapacity]; assert(elem != NULL); //存储分配失败则退出; } template<typename T> Vector<T>::Vector(std::initializer_list<T> l) //列表初始化,新标准 { thesize = l.size(); thecapacity = thesize + SPARE_CAPACITY; elem = new T[thecapacity]; assert(elem != NULL); int i = 0; auto beg = l.begin(); while (beg != l.end() && i != thesize) { elem[i] = *beg; ++i; ++beg; } } template <typename T> Vector<T>::Vector(int initsize, T value) :thesize(initsize), thecapacity(initsize + SPARE_CAPACITY) { elem = new T[thecapacity]; assert(elem != NULL); //存储分配失败则退出; for (int i = 0; i != thesize; ++i) elem[i] = value; } template <typename T> Vector<T>::Vector(iterator b, iterator e) { thesize = e - b; thecapacity = thesize + SPARE_CAPACITY; elem = new T[thecapacity]; assert(elem != NULL); for (int i = 0; b != e&&i != thesize; ++i) { elem[i] = *b; ++b; } } //拷贝构造函数，接受一个容器为另一个容器的拷贝（深拷贝） template <typename T> Vector<T>::Vector(const Vector &rhs) { thesize = rhs.thesize; thecapacity = rhs.thecapacity; elem = new T[thecapacity]; assert(elem != NULL); for (int i = 0; i != thesize; ++i) elem[i] = rhs.elem[i]; } //赋值运算符 template<typename T> Vector<T>& Vector<T>::operator=(const Vector &rhs) { if (this != &rhs) //防止自赋值 { delete[]elem; thesize = rhs.thesize; thecapacity = rhs.thecapacity; elem = new T[thecapacity]; assert(elem != NULL); for (int i = 0; i != thesize; ++i) elem[i] = rhs.elem[i]; } return *this; } //swap函数的实现，通常比从一个向另一个容器拷贝元素快，只是交换了两个容器内部的数据结构，元素本身没有交换。。 //交换的是相同类型的容器。 //assign，赋值函数的实现 /********************************************关系运算符**********************************/ //关系运算符的实现==，！=，> ,>=, <, <= template<typename T> bool Vector<T>::operator==(const Vector<T>& rhs) { if (this->thesize == rhs.thesize) //与容量没有关系 { int cnt = 0; for (int i = 0; i != thesize; i++) if (this->elem[i] == rhs.elem[i]) ++cnt; if (cnt == thesize) return true; } return false; } template<typename T> bool Vector<T>::operator!=(const Vector<T>& rhs) { return !(*this == rhs); } //分配至少容纳newcapacity个的元素空间 template<typename T> void Vector<T>::reserve(int newcapacity) { if (newcapacity <= thecapacity) { if (newcapacity < thecapacity / 2) //当新的容量很小时 { T *newarray = new T[newcapacity]; int newsize = newcapacity > thesize ? thesize : newcapacity; for (int i = 0; i != newsize; ++i) newarray[i] = elem[i]; delete[] elem; elem = newarray; thecapacity = newcapacity; } return; } T *newarray = new T[newcapacity]; for (int i = 0; i != thesize; ++i) newarray[i] = elem[i]; delete[] elem; elem = newarray; thecapacity = newcapacity; } //调整它的大小，若newsize<thesize，多的元素被丢弃，若相反，添加新元素，新添进来的元素初始化为thevalue template<typename T> void Vector<T>::resize(int newsize, const T & thevalue) { if (newsize > thesize) { if (newsize > thecapacity) reserve(newsize * 2 + 1); for (int i = thesize; i != newsize; ++i) //新添进来的元素初始化为thevalue elem[i] = thevalue; } else if (newsize< thesize) { if (newsize<thecapacity / 2) reserve(newsize); } thesize = newsize; } template<typename T> void Vector<T>::resize(int newsize) //调整它的大小，若newsize<thesize，多的元素被丢弃，若相反，添加新元素，进行值初始化 { resize(newsize, T()); } template<typename T> void Vector<T>::shrink_to_fit() //将capacity（）减少为与size（）相同大小 { reserve(thesize + SPARE_CAPACITY); } /**************************************访问操作***************************************/ template<typename T> T & Vector<T>::operator[](int index) { if (index < 0 || index >= thesize) { cout << "下标超出范围" << endl; return; } return elem[index]; } template<typename T> const T &Vector<T>::operator[](int index) const //返回下标不能修改 { if (index < 0 || index >= thesize) { cout << "下标超出范围" << endl; return; } return elem[index]; } template<typename T> T& Vector<T>::front() { if (!this->empty()) return elem[0]; } template<typename T> const T& Vector<T>::front() const { if (!this->empty()) return elem[0]; } template<typename T> T& Vector<T>::back() { if (!this->empty()) return elem[thesize - 1]; } template<typename T> const T& Vector<T>::back() const { if (!this->empty()) return elem[thesize - 1]; } /******************************************插入操作*************************************/ //向容器插入元素，vector不支持push_front,但insert可以实现插入vector的任何位置，但是注意在vector除尾部之外的任何位置很慢，很耗时。。 template<typename T> void Vector<T>::push_back(const T &x) { if (thesize == thecapacity) reserve(2 * thecapacity); elem[thesize++] = x; } template<typename T> T* Vector<T>::insert(iterator b, const T &value) //返回类型为Vector<T>::iterator则出错？？ { if (b < this->begin() || b> this->end()) //b可以为尾后迭代器 { cout << "超出范围" << endl; exit(0); } int num = b - elem; if (thesize == thecapacity) { reserve(thesize * 2); b = elem + num; //重新分配内存后原来的指针b失效了，所以此处令b指向新分配的数组中 } for (iterator p = this->end(); p > b; p--) *p = *(p - 1); *b = value; thesize++; return b; } //删除操作 template<typename T> T* Vector<T>::erase(iterator b) { if (b < this->begin() || b >= this->end()) //确保迭代器在范围内，否则未定义，b不能为尾后迭代器 { cout << "超出范围" << endl; exit(0); } iterator q = b + 1; int num = q - elem; iterator p = this->end() - 1; for (; b < p; b++) *b = *(b + 1); thesize--; if (thesize <= thecapacity / 4) //防止删除后空闲空间太大，浪费空间 { reserve(thesize + SPARE_CAPACITY); iterator q1 = elem + num; //重新进行内存分配后原来的指针q可能失效了 return q1; } return q; } template<typename T> void Vector<T>::clear() { thesize = 0; } #endif
附上测试代码：
#include <string> #include<iostream> #include"Vector.h" //注意当这里不是标准库的头文件，是自己写的，要用双引号，整了好久，还以为程序出错了。。 using namespace std; int main() { Vector<int> v1; Vector<int> v2(5, 9); Vector<int> v3(v2); Vector<int> v4(v2.begin(), v2.end()); if (v1.empty()) cout <<"v1为空，大小为："<< v1.size() << endl; cout << "向v1插入元素："; int a; while (cin >> a) v1.push_back(a); if (!v1.empty()) cout << "v1不为空,大小为:" << v1.size() << "容量为：" << v1.capacity() << endl; cout << "元素为："; for (Vector<int>::iterator iter = v1.begin(); iter != v1.end(); ++iter) cout << *iter << " "; cout << endl; cout << "重新插入后："; v1.insert(v1.begin() + 1, 4); cout << "此时v1大小为:" << v1.size() << "容量为：" << v1.capacity() << endl; cout << "元素为："; for (Vector<int>::iterator iter = v1.begin(); iter != v1.end(); ++iter) cout << *iter << " "; cout << endl; cout << "删除元素后为："; v1.pop_back(); for (Vector<int>::iterator iter = v1.begin(); iter != v1.end(); ++iter) cout << *iter << " "; cout << endl; cout << "再次删除元素后为："; v1.erase(v1.begin() + 2); for (Vector<int>::iterator iter = v1.begin(); iter != v1.end(); ++iter) cout << *iter << " "; cout << endl; cout << "v2元素为："; for (Vector<int>::iterator iter = v2.begin(); iter != v2.end(); ++iter) cout << *iter << " "; cout << endl; cout << "v3元素为："; for (Vector<int>::iterator iter = v3.begin(); iter != v3.end(); ++iter) cout << *iter << " "; cout << endl; cout << "v4元素为："; for (Vector<int>::iterator iter = v4.begin(); iter != v4.end(); ++iter) cout << *iter << " "; cout << endl; if (v1 == v3) cout << "v1与v3相等"; else cout << "v1与v3不相等" << endl; Vector<int> v = { 1, 2, 3, 4, 5 }; Vector<int> v5; v5 = v; cout << "v5元素为："; for (Vector<int>::iterator iter = v5.begin(); iter != v5.end(); ++iter) cout << *iter << " "; cout << endl; v5.push_back(99); v5.resize(2, 2); cout << "操作后v5元素为："; for (Vector<int>::iterator iter = v5.begin(); iter != v5.end(); ++iter) cout << *iter << " "; cout << endl; std::cout << v5.capacity() << "\n"; return 0; }
运行结果：
