C++:模拟实现STL的vector
目录
一.vector类
1.vector类的构造及析构
2.定义迭代器
3.size()和capacity()
4.operator [ ]
5.resize()和reserve()
6.插入和删除
二.整体代码
1.vector.h
2.vector.cpp
上一节中了解了vector中部分接口的使用,在这里我们模拟实现vector,为了避免与库中的起冲突,在这里使用命名空间
一.vector类
1.vector类的构造及析构
vector类中我们有三个对象_start,_finish,_endofstorage
构造函数
vector() :_start(nullptr), _finish(nullptr), _endofstorage(nullptr)
{}拷贝构造
vector(const vector<T>& v)
{
_start = new T[v.capacity()];
_finish = _start;
_endofstorage = _start + v.capacity();
for (size_t i = 0; i < v.size(); ++i)
{
*_finish = v[i];
++_finish;
}
}但是我们可以采取一个更简单的方法,将值插入要拷贝的对象中
//v2(v1)
vector(const vector<T>& v):_start(nullptr), _finish(nullptr), _endofstorage(nullptr)
{
//将v1的数据插入v2
for (const auto& ch : v)
{
reserve(v.capacity());
push_back(ch);
}
}赋值
我们可以选择将两个的值进行交换
vector<T>& operator=(vector<T> v)
{
swap(v);
return *this;
}
void swap(vector<T>& v)
{
::swap(_start, v._start);
::swap(_finish, v._finish);
::swap(_endofstorage, v._endofstorage);
}析构
~vector()
{
delete[] _start;
_start = _finish = _endofstorage = nullptr;
}2.定义迭代器
typedef T* iterator;
typedef const T* const_iterator;
iterator begin()
{
return _start;
}
iterator end()
{
return _finish;
}
const_iterator begin() const
{
return _start;
}
const_iterator end() const
{
return _finish;
}3.size()和capacity()
所以size只需要用_finish-_start,capacity用_endofstorage-_start
size_t size() const
{
return _finish - _start;
}
size_t capacity() const
{
return _endofstorage - _start;
}4.operator [ ]
T& operator[](size_t i)
{
assert(i < size());
return _start[i];
}
const T& operator[](size_t i) const
{
assert(i < size());
return _start[i];
}5.resize()和reserve()
void reserve(size_t n)
{
if (n > capacity())
{
size_t sz = size();
T* tmp = new T[n];
if (_start)
{
//memcpy(tmp, _start, sizeof(T) * sz);按字节拷贝,浅拷贝
for (size_t i = 0; i < sz; ++i)
{
tmp[i] = _start[i];//调用operator=深拷贝
}
delete[] _start;
}
_start = tmp;
_finish = tmp + sz;
_endofstorage = tmp + n;
}
}
void resize(size_t n, const T& val = T())
{
if (n < size())
{
_finish = _start + n;
}
else
{
if (n > capacity())
{
reserve(n);
}
while (_finish < _start + n)
{
*_finish = val;
++_finish;
}
}
}6.插入和删除
push_back
当容量不足时开辟新空间,在尾部插入即可,同时将_finish向后移动
void push_back(const T& x)
{
if (_finish == _endofstorage)
{
size_t newcapacity = capacity() == 0 ? 2 : capacity() * 2;
reserve(newcapacity);
}
*_finish = x;
++_finish;
}pop_back
直接将_finish后移即可
void pop_back()
{
assert(_start < _finish);
--_finish;
}insert
void insert(iterator pos, const T& x)
{
assert(pos <= _finish);
if (_finish == _endofstorage)
{
size_t n = pos - _start;
size_t newcapacity = capacity() == 0 ? 2 : capacity() * 2;
reserve(newcapacity);
//如果增容原来的pos就失效了,需要重新计算位置
pos = _start + n;
}
iterator end = _finish - 1;
while (end >= pos)
{
*(end + 1) = *end;
--end;
}
*pos = x;
++_finish;
}当我们实现insert后,push_back就可以用复用实现
void push_back(const T& x)
{
insert(_finish, x);
}erase
iterator erase(iterator pos)
{
assert(pos < _finish);
iterator it = pos;
while (it < _finish)
{
*it = *(it + 1);
++it;
}
--_finish;
return pos;
}同样实现了erase,pop_back也可以复用
void pop_back()
{
erase(_finish - 1);
}二.整体代码
1.vector.h
#pragma once
#include<iostream>
#include<assert.h>
using namespace std;
namespace wzyl
{
template<class T>
class vector
{
public:
typedef T* iterator;
typedef const T* const_iterator;
vector() :_start(nullptr), _finish(nullptr), _endofstorage(nullptr)
{}
/*vector(const vector<T>& v)
{
_start = new T[v.capacity()];
_finish = _start;
_endofstorage = _start + v.capacity();
for (size_t i = 0; i < v.size(); ++i)
{
*_finish = v[i];
++_finish;
}
}*/
//v2(v1)
vector(const vector<T>& v):_start(nullptr), _finish(nullptr), _endofstorage(nullptr)
{
//将v1的数据插入v2
for (const auto& ch : v)
{
reserve(v.capacity());
push_back(ch);
}
}
vector<T>& operator=(vector<T> v)
{
swap(v);
return *this;
}
void swap(vector<T>& v)
{
::swap(_start, v._start);
::swap(_finish, v._finish);
::swap(_endofstorage, v._endofstorage);
}
~vector()
{
delete[] _start;
_start = _finish = _endofstorage = nullptr;
}
iterator begin()
{
return _start;
}
iterator end()
{
return _finish;
}
const_iterator begin() const
{
return _start;
}
const_iterator end() const
{
return _finish;
}
void reserve(size_t n)
{
if (n > capacity())
{
size_t sz = size();
T* tmp = new T[n];
if (_start)
{
//memcpy(tmp, _start, sizeof(T) * sz);按字节拷贝,浅拷贝
for (size_t i = 0; i < sz; ++i)
{
tmp[i] = _start[i];//调用operator=深拷贝
}
delete[] _start;
}
_start = tmp;
_finish = tmp + sz;
_endofstorage = tmp + n;
}
}
void resize(size_t n, const T& val = T())
{
if (n < size())
{
_finish = _start + n;
}
else
{
if (n > capacity())
{
reserve(n);
}
while (_finish < _start + n)
{
*_finish = val;
++_finish;
}
}
}
void push_back(const T& x)
{
/*if (_finish == _endofstorage)
{
size_t newcapacity = capacity() == 0 ? 2 : capacity() * 2;
reserve(newcapacity);
}
*_finish = x;
++_finish;*/
insert(_finish, x);
}
void pop_back()
{
/*assert(_start < _finish);
--_finish;*/
erase(_finish - 1);
}
void insert(iterator pos, const T& x)
{
assert(pos <= _finish);
if (_finish == _endofstorage)
{
size_t n = pos - _start;
size_t newcapacity = capacity() == 0 ? 2 : capacity() * 2;
reserve(newcapacity);
//如果增容原来的pos就失效了,需要重新计算位置
pos = _start + n;
}
iterator end = _finish - 1;
while (end >= pos)
{
*(end + 1) = *end;
--end;
}
*pos = x;
++_finish;
}
iterator erase(iterator pos)
{
assert(pos < _finish);
iterator it = pos;
while (it < _finish)
{
*it = *(it + 1);
++it;
}
--_finish;
return pos;
}
T& operator[](size_t i)
{
assert(i < size());
return _start[i];
}
const T& operator[](size_t i) const
{
assert(i < size());
return _start[i];
}
size_t size() const
{
return _finish - _start;
}
size_t capacity() const
{
return _endofstorage - _start;
}
private:
iterator _start;
iterator _finish;
iterator _endofstorage;
};
void test_vector1()
{
vector<int> v;
v.push_back(1);
v.push_back(2);
v.push_back(3);
v.push_back(4);
v.push_back(5);
cout << v.size() << endl;
cout << v.capacity() << endl;
vector<int>::iterator it = v.begin();
while (it != v.end())
{
cout << *it << " ";
++it;
}
cout << endl;
for (auto& ch : v)
{
cout << ch << " ";
}
cout << endl;
for (size_t i = 0; i < v.size(); ++i)
{
cout << v[i] << " ";
}
cout << endl;
}
void test_vector2()
{
vector<int> v;
v.push_back(1);
v.push_back(2);
v.push_back(3);
v.push_back(4);
v.push_back(5);
v.push_back(6);
v.insert(v.begin(), 0);
for (auto& ch : v)
{
cout << ch << " ";
}
cout << endl;
vector<int>::iterator it = v.begin();
while (it != v.end())
{
if (*it % 2 == 0)
{
it = v.erase(it);
}
else
{
++it;
}
}
for (auto ch : v)
{
cout << ch << " ";
}
cout << endl;
}
void test_vector3()
{
vector<int> v;
v.reserve(10);
v.push_back(1);
v.push_back(2);
v.push_back(3);
v.push_back(4);
v.push_back(5);
v.push_back(6);
for (auto ch : v)
{
cout << ch << " ";
}
cout << endl;
cout << v.size() << endl;
cout << v.capacity() << endl << endl;
v.resize(4);
for (auto ch : v)
{
cout << ch << " ";
}
cout << endl;
cout << v.size() << endl;
cout << v.capacity() << endl << endl;
v.resize(8);
for (auto ch : v)
{
cout << ch << " ";
}
cout << endl;
cout << v.size() << endl;
cout << v.capacity() << endl << endl;
v.resize(12);
for (auto ch : v)
{
cout << ch << " ";
}
cout << endl;
cout << v.size() << endl;
cout << v.capacity() << endl << endl;
}
void test_vector4()
{
vector<int> v1;
v1.push_back(1);
v1.push_back(2);
v1.push_back(3);
v1.push_back(4);
vector<int> v2(v1);
for (auto ch : v1)
{
cout << ch << " ";
}
cout << endl;
for (auto ch : v2)
{
cout << ch << " ";
}
cout << endl;
vector<int> v3;
v3.push_back(10);
v3.push_back(20);
v3.push_back(30);
v3.push_back(40);
v1 = v3;
for (auto ch : v1)
{
cout << ch << " ";
}
cout << endl;
}
}2.vector.cpp
#include"vector.h"
int main()
{
//wzyl::test_vector1();
//wzyl::test_vector2();
//wzyl::test_vector3();
//wzyl::test_vector4();
}