C++拓展了面向對象和模板
STL分兩大部分:容器,算法
函數模板
//任意類型的選擇排序
template <typename T>
void sort(T arr[], int len)
{
for (int i = 0; i < len - 1; ++i)
{
for (int j = i + 1; j < len; ++j)
{
if (arr[i] > arr[j])
{
T tempVal = arr[i];
arr[i] = arr[j];
arr[j] = tempVal;
}
}
}
}
容器
vector deque list map (set multiset multimap)
分爲兩類:
1、序列式容器 是可序羣集,每個元素都有固定的位置,元素的位置取決於插入的時機和地點,和元素值無關(vector deque list)
2、關係(聯)式容器 是已序羣集 元素的位置取決於元素值和特定的排序規律 (set map multiset multimap)
優劣:
元素進入容器,序列式優於關係式
搜索元素時,關係式優於序列式
查找:
二分查找(折半查找)
STL容器必須滿足以下條件:
1、容器進行元素的插入操作,內部實現的是拷貝操作,因此STL容器內的每一個元素都必須能夠被拷貝
2、所有的元素形成次序,也就是說多次遍歷每個元素時的次序總是相同的
3、一般而言,各項操作並非絕對安全,調用者必須確保傳給操作函數的參數符合需求
迭代器:可遍歷stl容器內全部或部分元素的一個對象,對象行爲理解爲指針(智能指針)
vector
動態數組(c++標準並沒有要求必須用動態數組來實現vector,只是規定了相應的條件和操作複雜度)
使用案例:
vector<int> v;//定義了一個對象,這個對象就是一個動態數組
for (int i = 0; i < 10; ++i)
v.push_back(i + 1);//分配空間的事情,賦值的事情
for (int i = 0; i < 10; ++i)
printf("%d\n",v[i]);
vector<int>::iterator vit = v.begin();//vector的迭代器
v.insert(vit + 2, 100);
vit = vit + 3;
v.erase(vit);
for (vit = v.begin(); vit != v.end(); ++vit)
printf("%d\n",*vit);
vector是一個動態數組,支持隨機存取,只要知道位置,很方便直接存取這個位置的元素
在尾部進插入和刪除元素時,性能是比較高,在前端和中部進行插入和刪除,性能相對比較差,要做大量的移位
容器大小可以變化,注意:如果大小發生變化,可能會導致內存重新分配。重分配會有什麼後果?
棧鏈式棧(鏈表) 順序棧(數組)
STL容器並非絕對安全,比如越界等等
T模板函數遇到問題不能return,只能拋異常throw
assert(nullptr);//斷言函數,當參數爲空觸發斷點
C++有接口用類,只有運算符重載和成員用結構,習慣
注意內存重分配後地址變了要返回迭代器
系統vector在刪除時會導致內存重分配
手撕Vector
例子的vector內存是連續(通過new),系統vector內存未必連續
#pragma once
//動態數組
//template<class T>
template<typename T>
class CMyVector
{
T *pBuff;//給出一個指針,用來指向一個動態內存
unsigned int len;//給一個長度,表示這個動態內存中的元素個數
size_t maxSize;//這個動態內存最大的空間大小,也是U_int
public:
struct MyIterator//這個結構也是一個模板,一個模板內部嵌套定義了一個模板
{
T *pIt;
MyIterator & operator = (MyIterator const& srcIt)
{
pIt = srcIt.pIt;
return *this;
}
bool operator!=(MyIterator const& srcIt) const
{
return pIt != srcIt.pIt;
}
MyIterator & operator++()//前置
{
pIt++;
return *this;
}
MyIterator operator++(int)//後置
{
MyIterator tempIt = *this;
pIt++;
return tempIt;
}
T &operator*()
{
return *pIt;
}
int operator-(MyIterator const & scrIt) const
{
return pIt - scrIt.pIt;
}
MyIterator operator +(int n)
{
MyIterator tempIt = *this;
tempIt.pIt += n;
return tempIt;
}
};
public:
MyIterator begin()//得到容器的第一個位置
{
MyIterator tempIt;
tempIt.pIt = pBuff;
return tempIt;
}
MyIterator end()//得到容器的最後一個元素的下一個位置
{
MyIterator tempIt;
tempIt.pIt = pBuff + len;
return tempIt;
}
public:
MyIterator insert(MyIterator const& pos, MyIterator const& first, MyIterator const& second)
{
MyIterator tempIt = pos;
int n = second - first;
for (int i = 0; i < n; ++i)
tempIt = insert(tempIt, *(first + i));
return tempIt;
}
MyIterator insert(MyIterator const& pos, int n, T const & elem)//在pos處插入n個elem元素
{
MyIterator tempIt = pos;
for (int i = 0; i < n; ++i)
tempIt = insert(tempIt, elem);
return tempIt;
}
MyIterator insert(MyIterator const& pos, T const& elem)//插入,在pos這個迭代器所指的位置插入一個elem元素
{
int index = pos.pIt - pBuff;//通過迭代器位置和容器的首地址進行相減,得到當前的下標
if (len >= maxSize)
{
maxSize = maxSize + ((maxSize >> 1) > 1 ? (maxSize >> 1) : 1);
T *tempBuff = new T[maxSize];
for (size_t i = 0; i < len; ++i)
tempBuff[i] = pBuff[i];
if (pBuff != nullptr)
delete[] pBuff;
pBuff = tempBuff;
}
//移位
for (size_t i = len; i > index; --i)
{
pBuff[i] = pBuff[i - 1];
}
pBuff[index] = elem;
len++;
MyIterator tempIt;
tempIt.pIt = pBuff + index;
return tempIt;
}
//注意:自己模擬的動態數組在元素刪除時不會有內存重分配,但是系統vector在刪除時會導致內存重分配
MyIterator erase(MyIterator const& pos)
{
int index = pos.pIt - pBuff;
for (size_t i = index; i < len - 1; ++i)
{
pBuff[i] = pBuff[i + 1];
}
len--;
MyIterator tempIt;
tempIt.pIt = pBuff + index;
return tempIt;
}
MyIterator erase(MyIterator const& first, MyIterator const& second)
{
int n = second - first;
MyIterator tempIt = first;
for (int i = 0; i < n; ++i)
tempIt = erase(tempIt);
return tempIt;
}
public:
CMyVector();
CMyVector(int n);//有n個用T的默認構造構造的對象,構造進這個容器
CMyVector(int n, T const& elem);//用n個elem對象,構造進這個容器
CMyVector(CMyVector const& other);
~CMyVector();
void clear();//清除
public:
size_t size() const;
size_t capacity() const;//返回容器大小
bool empty() const;//判斷容器是否爲空
public:
bool operator==(CMyVector const& srcVector) const;
bool operator!=(CMyVector const& srcVector) const;
//作業:實現>,>=,<,<=運算符重載(規則:參照strcmp)
//作業:實現自身類和參數類交換,要求必須有2個參數
public:
void assign(int n, T const& elem);//賦值
void swap(CMyVector & srcVector);//交換
public:
T at(int index);//返回動態數組中下標爲index的元素
T operator[](int index);
T front();//得到容器中的第一個元素,不管容器爲不爲空
T back();
public:
void push_back(T const& elem);//往動態數組尾部進行添加數據
void pop_back();//從動態數組的尾部進入刪除數據
public:
void resize(int num);//將元素的數量len改爲num這個數量,如果size()變大了,多出來的將用默認構造來創建
void resize(int num, T const& elem);
void reserve(int num);//如果容器的容量不足,擴大容量
};
template<typename T>
void CMyVector<T>::reserve(int num)
{
if (num > maxSize)
{
maxSize = num;
T * tempBuff = new T[maxSize];
for (size_t i = 0; i < len; ++i)
tempBuff[i] = pBuff[i];
if (pBuff != nullptr)
delete[] pBuff;
pBuff = tempBuff;
}
}
template<typename T>
void CMyVector<T>::resize(int num, T const& elem)
{
if (num < 0)
assert(nullptr);//斷言函數
if (num > len)
{
while (num >= maxSize)
maxSize = maxSize + ((maxSize >> 1) > 1 ? (maxSize >> 1) : 1);
T *tempBuff = new T[maxSize];
for (size_t i = 0; i < len; ++i)
tempBuff[i] = pBuff[i];
if (pBuff != nullptr)
delete[] pBuff;
pBuff = tempBuff;
for (size_t i = len; i < num; ++i)
pBuff[i] = elem;
}
len = num;
}
template<typename T>
void CMyVector<T>::resize(int num)
{
if (num < 0)
assert(nullptr);//斷言函數
if (num > len)
{
while (num >= maxSize)
maxSize = maxSize + ((maxSize >> 1) > 1 ? (maxSize >> 1) : 1);
T *tempBuff = new T[maxSize];
for (size_t i = 0; i < len; ++i)
tempBuff[i] = pBuff[i];
if (pBuff != nullptr)
delete[] pBuff;
pBuff = tempBuff;
}
len = num;
}
template<typename T>
void CMyVector<T>::pop_back()
{
--len;
}
template<typename T>
void CMyVector<T>::push_back(T const& elem)
{
//1 2 3 4 6 9 13 19
if (len >= maxSize)
{
maxSize = maxSize + ((maxSize >> 1) > 1 ? (maxSize >> 1) : 1);
T *tempBuff = new T[maxSize];
for (size_t i = 0; i < len; ++i)
tempBuff[i] = pBuff[i];
if (pBuff != nullptr)
delete[] pBuff;
pBuff = tempBuff;
}
pBuff[len++] = elem;
}
template<typename T>
T CMyVector<T>::back()
{
return pBuff[len - 1];
}
template<typename T>
T CMyVector<T>::front()
{
return pBuff[0];
}
template<typename T>
T CMyVector<T>::operator[](int index)
{
return pBuff[index];
}
template<typename T>
T CMyVector<T>::at(int index)//唯一的會主動拋異常的函數
{
if (index < 0 || index >= len)
throw "out_of_range";
return pBuff[index];
}
template<typename T>
void CMyVector<T>::swap(CMyVector & srcVector)
{
T *tempBuff = pBuff;
size_t tempLen = len;
size_t tempMaxSize = maxSize;
pBuff = srcVector.pBuff;
len = srcVector.len;
maxSize = srcVector.maxSize;
srcVector.pBuff = tempBuff;
srcVector.len = tempLen;
srcVector.maxSize = tempMaxSize;
}
template<typename T>
void CMyVector<T>::assign(int n, T const& elem)
{
clear();//重點:清除自身可能原有的動態內存
if (n > 0)
{
len = maxSize = n;
pBuff = new T[maxSize];
for (size_t i = 0; i < len; ++i)
pBuff[i] = elem;
}
}
template<typename T>
bool CMyVector<T>::operator!=(CMyVector const& srcVector) const
{
return !(*this == srcVector);
}
template<typename T>
bool CMyVector<T>::operator==(CMyVector const& srcVector) const
{
if (len != srcVector.len)
return false;
for (size_t i = 0; i < len; ++i)
{
if (pBuff[i] != srcVector.pBuff[i])
return false;
}
return true;
}
template<typename T>
bool CMyVector<T>::empty() const
{
//return pBuff == nullptr;
return len == 0;
}
template<typename T>
size_t CMyVector<T>::capacity() const
{
return maxSize;
}
template<typename T>
size_t CMyVector<T>::size() const
{
return len;
}
template<typename T>
CMyVector<T>::CMyVector(CMyVector const& other)
{
len = other.len;
maxSize = other.maxSize;
pBuff = nullptr;
if (len > 0)
{
pBuff = new T[maxSize];
for (int i = 0; i < len; ++i)
pBuff[i] = other.pBuff[i];
}
}
template<typename T>
CMyVector<T>::CMyVector(int n, T const& elem)
{
if (n <= 0)
{
pBuff = nullptr;
len = 0;
maxSize = 0;
}
else
{
len = maxSize = n;
pBuff = new T[maxSize];
for (size_t i = 0; i < len; ++i)
pBuff[i] = elem;
}
}
template<typename T>
CMyVector<T>::CMyVector(int n)
{
if (n <= 0)
{
pBuff = nullptr;
len = 0;
maxSize = 0;
}
else
{
len = maxSize = n;
pBuff = new T[maxSize];
}
}
template<typename T>
void CMyVector<T>::clear()
{
if (pBuff != nullptr)
delete[] pBuff;
pBuff = nullptr;
len = 0;
maxSize = 0;
}
template<typename T>
CMyVector<T>::~CMyVector()
{
clear();
}
template<typename T>
CMyVector<T>::CMyVector()
{
pBuff = nullptr;
len = 0;
maxSize = 0;
}