【C++】vector 常用成员函数的模拟实现

1. vector 常用成员函数的模拟实现

2. vector 常用成员函数实现后的测试

#include<assert.h>
#include<iostream>
#include<string>
using std::cout;
using std::endl;
using std::string;

//自定义命名空间wch
namespace wch
{
//vector要支持不同类型元素，所以用模板
template<class T>

class vector
{
public:
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;
}

// vector<int> v(10, 1);//如果无函数vector(int n, const T& val = T())，
//因为参数类型更匹配，会去调用vector(InputIterator first, InputIterator last)
// 但是函数内部有解引用（*first），整形不可解引用，导致报错
vector(size_t n, const T& val = T())
{
resize(n, val);
}
vector(int n, const T& val = T())
{
resize(n, val);
}

// [first, last)迭代器，采用区间初始化
template<class InputIterator>
vector(InputIterator first, InputIterator last)
{
while (first != last)
{
push_back(*first);
++first;
}
}

//由于声明时已经初始化给予了缺省参数，所以此处不写初始化列表初始化
vector()
{}

//原始方法实现拷贝构造函数
vector(const vector<T>& v)
{
_start = new T[v.capacity()];
//memcpy(_start, v._start, sizeof(T)*v.size());//浅拷贝，部分自定义类型无法达到目的

//深拷贝
for (size_t i = 0; i < v.size(); i++)
{
_start[i] = v._start[i];
}

_finish = _start + v.size();
_endofstorage = _start + v.capacity();
}

//现代方法拷贝构造
/*vector(const vector<T>& v)
:_start(nullptr)
, _finish(nullptr)
, _endofstorage(nullptr)
{
reserve(v.capacity());
for (auto e : v)
{
push_back(e);
}
}*/

void swap(vector<T>& v)
{
//注意这里用的是库函数swap，因为我们这里是在自己实现vector成员函数
std::swap(_start, v._start);
std::swap(_finish, v._finish);
std::swap(_endofstorage, v._endofstorage);
}
// v1 = v2，赋值运算符重载
vector<T>& operator=(vector<T> v)
{
swap(v);
return *this;
}

~vector()
{
if (_start)
{
delete[] _start;
_start = _finish = _endofstorage = nullptr;
}
}

void reserve(size_t n)
{
//要加判断，因为当n<capacity时，不需要做处理
if (n > capacity())
{
//这里需要先保存大小，因为开辟新空间后，成员函数size里的地址_finish还指向销毁的旧空间，
//无法正确完成_finish的更新
size_t sz = size();
T* tmp = new T[n];
if (_start)
{
//memcpy(tmp, _start, sizeof(T) * sz);//浅拷贝

//深拷贝
for (size_t i = 0; i < sz; i++)
{
tmp[i] = _start[i];
}

delete[] _start;
}

_start = tmp;
_finish = _start + sz;
_endofstorage = _start + n;
}
}

//缺省参数T()，当缺省参数为自定义类型，T()为匿名对象，会去调用构造函数
//内置类型如：int与int()无差别
void resize(size_t n, const T& val = T())
{
if (n < size())
{
_finish = _start + n;
}
else
{
reserve(n);
//多余有效空间用val初始化
while (_finish != _start + n)
{
*_finish = val;
++_finish;
}
}
}

void push_back(const T& x)
{
/*if (_finish == _endofstorage)
{
size_t newcapacity = capacity() == 0 ? 4 : capacity() * 2;
reserve(newcapacity);
}

*_finish = x;
++_finish;*/
insert(end(), x);
}

void pop_back()
{
erase(--end());
}

size_t capacity() const
{
return _endofstorage - _start;
}

size_t size() const
{
return _finish - _start;
}

T& operator[](size_t pos)
{
assert(pos < size());

return _start[pos];
}
const T& operator[](size_t pos) const
{
assert(pos < size());

return _start[pos];
}

//返回插入元素地址
iterator insert(iterator pos, const T& x)
{
assert(pos >= _start && pos <= _finish);

if (_finish == _endofstorage)
{
size_t len = pos - _start;// 解决pos迭代器失效问题

size_t newcapacity = capacity() == 0 ? 4 : capacity() * 2;
reserve(newcapacity);

// 需要更新pos，因为扩容过后pos还指向旧空间，即解决pos迭代器失效问题
pos = _start + len;
}

iterator end = _finish - 1;
while (end >= pos)
{
*(end + 1) = *end;
--end;
}

*pos = x;
++_finish;

return pos;
}

//返回删除元素地址
iterator erase(iterator pos)
{
assert(pos >= _start && pos < _finish);

iterator it = pos + 1;
while (it != _finish)
{
*(it - 1) = *it;
++it;
}

--_finish;

return pos;
}

private:
//给予缺省参数
iterator _start = nullptr;
iterator _finish = nullptr;
iterator _endofstorage = nullptr;
};

void print(const vector<int>& v)
{
for (auto e : v)
{
cout << e << " ";
}
cout << endl;
}

void test_vector1()
{
vector<int> v1;
v1.push_back(1);
v1.push_back(2);
v1.push_back(3);
v1.push_back(4);
v1.push_back(5);

for (auto e : v1)
{
cout << e << " ";
}
cout << endl;

for (size_t i = 0; i < v1.size(); i++)
{
v1[i]++;
}

for (auto e : v1)
{
cout << e << " ";
}
cout << endl;

print(v1);
}

void test_vector2()
{
vector<int> v1;
v1.push_back(1);
v1.push_back(2);
v1.push_back(3);
v1.push_back(4);
v1.push_back(5);
v1.push_back(5);
v1.push_back(5);
v1.push_back(5);

for (auto e : v1)
{
cout << e << " ";
}
cout << endl;

v1.insert(v1.begin(), 100);

for (auto e : v1)
{
cout << e << " ";
}
cout << endl;

/*vector<int>::iterator p = v1.begin() + 3;
v1.insert(p, 300);*/

vector<int>::iterator p = v1.begin() + 3;
//v1.insert(p+3, 300);

// insert以后迭代器可能会失效(扩容)
// 记住，insert以后就不要使用这个形参迭代器了，因为他可能失效了
v1.insert(p, 300);

// 高危行为
// *p += 10;

for (auto e : v1)
{
cout << e << " ";
}
cout << endl;
}

void test_vector3()
{
vector<int> v1;
v1.push_back(1);
v1.push_back(2);
v1.push_back(2);
v1.push_back(3);
v1.push_back(4);
v1.push_back(5);
v1.push_back(6);

for (auto e : v1)
{
cout << e << " ";
}
cout << endl;

auto it = v1.begin();
while (it != v1.end())
{
if (*it % 2 == 0)
{
it = v1.erase(it);
}
else
{
++it;
}
}

//v1.erase(v1.begin());
//auto it = v1.begin()+4;
//v1.erase(it);

 erase以后，迭代器失效了，不能访问
 vs进行强制检查，访问会直接报错
//cout << *it << endl;
//++it;
//cout << *it << endl;

for (auto e : v1)
{
cout << e << " ";
}
cout << endl;
}

void test_vector4()
{
vector<int> v;
v.resize(10, 0);

for (auto e : v)
{
cout << e << " ";
}
cout << endl;

int i = 0;
int j = int();//i = 0;
int k = int(1);//k = 1;
}

void test_vector5()
{
vector<int> v;
v.push_back(1);
v.push_back(2);
v.push_back(3);
v.push_back(4);
v.push_back(5);

vector<int> v1(v);

for (auto e : v1)
{
cout << e << " ";
}
cout << endl;

vector<int> v2;
v2.resize(10, 1);

v1 = v2;
for (auto e : v1)
{
cout << e << " ";
}
cout << endl;
}

void test_vector6()
{
vector<string> v;
v.push_back("111111111111111111");
v.push_back("222222222222222222");
v.push_back("333333333333333333");
v.push_back("444444444444444444");
v.push_back("555555555555555555");

for (auto& e : v)
{
cout << e << " ";
}
cout << endl;

vector<string> v1(v);
for (auto& e : v1)
{
cout << e << " ";
}
cout << endl;
}

void test_vector7()
{
vector<int> v(10, 1);
vector<string> v1(10, "1111");
vector<int> v2(10, 1);

for (auto e : v)
{
cout << e << " ";
}
cout << endl;

vector<int> v3(v.begin(), v.end());
for (auto e : v3)
{
cout << e << " ";
}
cout << endl;

string str("hello world");
vector<char> v4(str.begin(), str.end());
for (auto e : v4)
{
cout << e << " ";
}
cout << endl;

int a[] = { 16,2,77,29 };
vector<int> v5(a, a + 4);
for (auto e : v5)
{
cout << e << " ";
}
cout << endl;
}
}

int main()
{
//wch::test_vector1();
//wch::test_vector2();
//wch::test_vector3();
//wch::test_vector4();
//wch::test_vector5();
//wch::test_vector6();
wch::test_vector7();

return 0;
}

原文地址：https://blog.csdn.net/2303_80737493/article/details/142621798

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