【C++】C++ STL探索:Vector使用与背后底层逻辑（二）

//重点实现resize
void resize(size_t n, const T& val = T())
{
    //缩容
    if (n <= size())
    {
        //类似截断
        _finish = _start + n;
    }
    else
    {
        //提前扩容
        //大于capacity才起作用
        reserve(n);
        while (_finish < _start + n)
        {
            *_finish = val;
            _finish++;
        }
    }
}

string str="1111";//构造+拷贝构造-->优化 直接构造
const string& str1="1111";//构造临时对象，引用的是临时对象
vector<string>v;
v.push_back(str);
v.push_back(string("2222"));
v.push_back("33333");

vector<int> v1={1,2,3,4,5};
vector<int> v2({1,2,3,4,5}) //直接构造

void insert(iterator pos, const T& val)
    {
        assert(_start <= pos);
        assert(pos <= _finish);
        //考虑是否需要扩容
        //说明空间已经满了
        if (_finish == _end_of_storage)
        {
            reserve(capacity() == 0 ? 4 : capacity() * 2);
        }
        //开始移动数据
        iterator it = _finish - 1;
        while (it >= pos)
        {
            *(it + 1) = *it;
            it--;
        }
        *pos = val;
        _finish++;
    }

void test_vector()
{
    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(6);
    v1.push_back(7);
    v1.push_back(8);
    print_vector(v1);
    vector<int>::iterator it = v1.begin() + 3;
    v1.insert(it, 40);
    print_vector(v1);
    cout << *it << endl;
}

//迭代器实现erase
iterator erase(iterator pos)
{
    assert(_start <= pos);
    //删除不到_finish这个位置
    assert(pos < _finish);
    iterator it = pos+1;
    //it=pos+1=_finish就是最后一个位置
    while (it <= _finish)
    {
        *(it - 1) = *(it);
        it++;
    }
    _finish--;
    return pos;
}

vector<int> v1;
    v1.push_back(1);
    v1.push_back(2);
    v1.push_back(3);
    v1.push_back(4);
    v1.push_back(5);
    vector<int>::iterator it = v1.begin();
    while (it != v1.end())
    {
      if (*it % 2 == 0)
      {
        v1.erase(it);
      }
      ++it;
    }

vector<int> v1;
    v1.push_back(1);
    v1.push_back(2);
    v1.push_back(3);
    v1.push_back(4);
    v1.push_back(4);
    v1.push_back(5);
    vector<int>::iterator it = v1.begin();
    while (it != v1.end())
    {
      if (*it % 2 == 0)
      {
        v1.erase(it);
      }
      ++it;
    }

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(4);

vector<int>::iterator it = v1.begin();
while (it != v1.end())
{
    if (*it % 2 == 0)
    {
        v1.erase(it);
    }
    else
    {
        it++;
    }
}
print_vector(v1);

vector<int>::iterator it = v1.begin();
  while (it != v1.end())
  {
    if (*it % 2 == 0)
    {
      it=v1.erase(it);
    }
    else
    {
      it++;
    }
  }

void push_back(const T& val )
{
    insert(end(), val);
}

void pop_back()
{
    /*assert(!empty());
                --_finish;*/
    erase(end()-1);
}

void pop_back()
{
    /*assert(!empty());
                --_finish;*/
    erase(end()-1);
}

bool empty()
{
    return _start == _finish;
}

void print_vector(const vector<T>& v)
{
    //下标加[]
    for (size_t i = 0; i < v.size(); i++)
    {
        cout << v[i] << " ";
    }
    cout << endl;
    //迭代器
    vector<T>::const_iterator it = v.begin();
    while (it != v.end())
    {
        cout << *it << " ";
        ++it;
    }
    cout << endl;
    //范围for
    for (auto e : v)
    {
        cout << e << " ";
    }
    cout << endl;、
}

typename vector<T>::const_iterator it = v.begin();
auto it = v.begin();
while (it != v.end())
{
    cout << *it << " ";
    ++it;
}
cout << endl;