2.4 Vector＜T＞动态数组（随机访问迭代器）

C++自学精简教程目录(必读)

该 Vector 版本特点

这里的版本主要是使用模板实现、支持随机访问迭代器，支持std::sort等所有STL算法。(本文对随机迭代器的支持参考了复旦大学大一公共基础课C++语言的一次作业)

随机访问迭代器的实现主要是继承std::iterator<std::random_access_iterator_tag, T>来实现的。

随机访问迭代器最牛逼的两个接口是：

friend iterator operator+(const iterator& lhs, size_t n);

friend iterator operator-(const iterator& lhs, size_t n);

问题解答

1 为何下面代码中的iterator是struct而不是class？

答：参考struct与class

题目代码

头文件 Vector.h ：

#ifndef VEC_H
#define VEC_H
#include <iostream>
#include <cassert>
#include <initializer_list>
//------下面的代码是用来测试你的代码有没有问题的辅助代码，你无需关注------
#include <algorithm>
#include <cstdlib>
#include <iostream> 
#include <vector>
#include <utility>
using namespace std;
struct Record { Record(void* ptr1, size_t count1, const char* location1, int line1, bool is) :ptr(ptr1), count(count1), line(line1), is_array(is) { int i = 0; while ((location[i] = location1[i]) && i < 100) { ++i; } }void* ptr; size_t count; char location[100] = { 0 }; int line; bool is_array = false; bool not_use_right_delete = false; }; bool operator==(const Record& lhs, const Record& rhs) { return lhs.ptr == rhs.ptr; }std::vector<Record> myAllocStatistic; void* newFunctionImpl(std::size_t sz, char const* file, int line, bool is) { void* ptr = std::malloc(sz); myAllocStatistic.push_back({ ptr,sz, file, line , is }); return ptr; }void* operator new(std::size_t sz, char const* file, int line) { return newFunctionImpl(sz, file, line, false); }void* operator new [](std::size_t sz, char const* file, int line)
{return newFunctionImpl(sz, file, line, true);
}void operator delete(void* ptr) noexcept { Record item{ ptr, 0, "", 0, false }; auto itr = std::find(myAllocStatistic.begin(), myAllocStatistic.end(), item); if (itr != myAllocStatistic.end()) { auto ind = std::distance(myAllocStatistic.begin(), itr); myAllocStatistic[ind].ptr = nullptr; if (itr->is_array) { myAllocStatistic[ind].not_use_right_delete = true; } else { myAllocStatistic[ind].count = 0; }std::free(ptr); } }void operator delete[](void* ptr) noexcept { Record item{ ptr, 0, "", 0, true }; auto itr = std::find(myAllocStatistic.begin(), myAllocStatistic.end(), item); if (itr != myAllocStatistic.end()) { auto ind = std::distance(myAllocStatistic.begin(), itr); myAllocStatistic[ind].ptr = nullptr; if (!itr->is_array) { myAllocStatistic[ind].not_use_right_delete = true; } else { myAllocStatistic[ind].count = 0; }std::free(ptr); } }
#define new new(__FILE__, __LINE__)
struct MyStruct { void ReportMemoryLeak() { std::cout << "Memory leak report: " << std::endl; bool leak = false; for (auto& i : myAllocStatistic) { if (i.count != 0) { leak = true; std::cout << "leak count " << i.count << " Byte" << ", file " << i.location << ", line " << i.line; if (i.not_use_right_delete) { cout << ", not use right delete. "; }	cout << std::endl; } }if (!leak) { cout << "No memory leak." << endl; } }~MyStruct() { ReportMemoryLeak(); } }; static MyStruct my; void check_do(bool b, int line = __LINE__) { if (b) { cout << "line:" << line << " Pass" << endl; } else { cout << "line:" << line << " Ohh! not passed!!!!!!!!!!!!!!!!!!!!!!!!!!!" << " " << endl; exit(0); } }
#define check(msg)  check_do(msg, __LINE__);
//------上面的代码是用来测试你的代码有没有问题的辅助代码，你无需关注------template<typename T>
class Vector
{
public:/* 提供默认构造函数， 否则只能使用有参版本，这会带来不变例如，Vector<int> arr; 这样会报错，因为需要默认构造函数*/Vector(void);//如果类提供了非默认构造函数，编译器不会自动提供默认构造函数Vector(const Vector& from);// 复制构造函数Vector(T* start, T* end);//  非默认构造函数Vector(int count, int value);//2 非默认构造函数Vector(std::initializer_list<T> value_array){for (auto& item : value_array){push_back(item);}}Vector& operator = (const Vector& from);bool operator==(const Vector& other) const{//(1) your codereturn false;}//赋值操作符~Vector();//析构函数
public:int size(void) const;bool empty(void) const;const T& operator[] (size_t n) const;T& operator[] (size_t n);void push_back(const T& val);void clear(void);
private:void deep_copy_from(const Vector<T>& from);public:struct iterator : std::iterator<std::random_access_iterator_tag, T>{friend class  Vector;friend bool operator == (const iterator& lhs, const iterator& rhs) { return lhs.m_hold == rhs.m_hold; }friend bool operator != (const iterator& lhs, const iterator& rhs) { return !(lhs == rhs); }friend size_t operator - (const iterator& lhs, const iterator& rhs) { return lhs.m_hold - rhs.m_hold; }friend bool operator < (const iterator& lhs, const iterator& rhs) { return lhs.m_hold < rhs.m_hold; }friend bool operator > (const iterator& lhs, const iterator& rhs) { return lhs.m_hold > rhs.m_hold; }friend bool operator <= (const iterator& lhs, const iterator& rhs) { return !(lhs > rhs); }friend bool operator >= (const iterator& lhs, const iterator& rhs) { return !(lhs < rhs); }friend iterator operator + (const iterator& lhs, size_t n) { iterator itr; itr.m_hold = lhs.m_hold + n; return itr; }//随机访问迭代器牛逼的地方friend iterator operator - (const iterator& lhs, size_t n) { iterator itr; itr.m_hold = lhs.m_hold - n; return itr; }//随机访问迭代器牛逼的地方public://用于前置形式iterator& operator++() { m_hold = m_hold + 1; return *this; };iterator& operator--() { m_hold = m_hold - 1; return *this; };//用于后置形式iterator operator++(int) { iterator itr = *this; m_hold += 1; return itr; }iterator operator--(int) { iterator itr = *this; m_hold -= 1; return itr; }T& operator*() const//这里必须是const in C++14{return *m_hold;}private:T* m_hold;};struct const_iterator : std::iterator<std::random_access_iterator_tag, T>{friend class  Vector;friend bool operator == (const const_iterator& lhs, const const_iterator& rhs) { return lhs.m_hold == rhs.m_hold; }friend bool operator != (const const_iterator& lhs, const const_iterator& rhs) { return !(lhs == rhs); }friend size_t operator - (const const_iterator& lhs, const const_iterator& rhs) { return lhs.m_hold - rhs.m_hold; }friend bool operator < (const const_iterator& lhs, const const_iterator& rhs) { return lhs.m_hold < rhs.m_hold; }friend bool operator > (const const_iterator& lhs, const const_iterator& rhs) { return lhs.m_hold > rhs.m_hold; }friend bool operator <= (const const_iterator& lhs, const const_iterator& rhs) { return !(lhs > rhs); }friend bool operator >= (const const_iterator& lhs, const const_iterator& rhs) { return !(lhs < rhs); }friend const_iterator operator + (const const_iterator& lhs, size_t n) { const_iterator itr; itr.m_hold = lhs.m_hold + n; return itr; }//随机访问迭代器牛逼的地方friend const_iterator operator - (const const_iterator& lhs, size_t n) { const_iterator itr; itr.m_hold = lhs.m_hold - n; return itr; }//随机访问迭代器牛逼的地方public://用于前置形式const_iterator& operator++() { m_hold = m_hold + 1; return *this; };const_iterator& operator--() { m_hold = m_hold - 1; return *this; };//用于后置形式const_iterator operator++(int) { const_iterator itr = *this; m_hold += 1; return itr; }const_iterator operator--(int) { const_iterator itr = *this; m_hold -= 1; return itr; }const T& operator*() const{return *m_hold;}private:T* m_hold;};iterator begin() noexcept{iterator itr;itr.m_hold = empty() ? nullptr : &m_data[0];return itr;}const_iterator cbegin() const noexcept;iterator end() noexcept{iterator itr;itr.m_hold = empty() ? nullptr : &m_data[m_size];return itr;}const_iterator cend() const noexcept;
private:size_t m_size = 0;//当前元素数量size_t m_capacity = 0;//容量T* m_data = nullptr;//数据部分
};template<typename T>
Vector<T>::Vector(void)
{
}template<typename T>
Vector<T>::Vector(T * start, T * end)
{std::cout << "Vector(T* start, T* end)" << std::endl;assert(start != nullptr && end != nullptr);m_capacity = m_size = ((size_t)end - (size_t)start)/sizeof(T);//这里如果用int来存放可能会盛不下，size_t可以保证盛放的下assert(m_size > 0);m_data = new T[m_size];for (size_t i = 0; i < m_size; i++){m_data[i] = *start++;}
}
template<typename T>
Vector<T>::Vector(int count, int value)
{std::cout << "Vector(count, value)" << std::endl;if (count <= 0){throw std::runtime_error("size of vector to init must bigger than zero!");}m_data = new T[count];for (int i = 0; i < count; i++){m_data[i] = value;}m_capacity = m_size = count;
}
template<typename T>
Vector<T>& Vector<T>::operator=(const Vector<T>& from)
{std::cout << "Vector::operator=" << std::endl;if (this == &from){return *this;}//先释放自己的数据clear();deep_copy_from(from);return *this;
}template<typename T>
Vector<T>::~Vector()
{//(2) your code}
template<typename T>
int Vector<T>::size(void) const
{return m_size;
}
template<typename T>
bool Vector<T>::empty(void) const
{//(3) your codereturn false;//此处需要修改。
}
template<typename T>
const T& Vector<T>::operator[](size_t n) const
{//(4) your codestatic T t;//此处需要修改。return t;//此处需要修改。
}
template<typename T>
T& Vector<T>::operator[](size_t n)
{//(4) your codestatic T t;//此处需要修改。return t;//此处需要修改。
}
template<typename T>
void Vector<T>::push_back(const T & val)
{//(5) your code}template<typename T>
void Vector<T>::clear(void)
{//(6) your code
}template<typename T>
void Vector<T>::deep_copy_from(const Vector<T>& from)
{//(7) your code}template<typename T>
Vector<T>::Vector(const Vector& from)
{//(8) your code}template<typename T>
typename Vector<T>::const_iterator Vector<T>::cend() const noexcept
{const_iterator itr = const_iterator();//(9) your codereturn itr;
}template<typename T>
typename Vector<T>::const_iterator Vector<T>::cbegin() const noexcept
{const_iterator itr = const_iterator();//(10) your codereturn itr;
}#endif

测试代码main.cpp：

#include <iostream>
#include <algorithm>
#include "Vector.h"
#include <vector>template<typename T>
void print(const Vector<T>& v, const std::string& msg)
{std::cout << "The contents of " << msg.c_str() << " are:";for (int i = 0; i < v.size(); ++i){std::cout << ' ' << v[i];}std::cout << '\n';
}
template<typename T>
void print_itr(Vector<T>& v, const std::string& msg)
{std::cout << "The contents of " << msg.c_str() << " are:";for (auto itr = v.begin(); itr != v.end(); ++itr){std::cout << ' ' << *itr;}std::cout << '\n';
}
template<typename T>
void print_const_itr(const Vector<T>& v, const std::string& msg)
{std::cout << "The contents of " << msg.c_str() << " are:";for (auto itr = v.cbegin(); itr != v.cend(); ++itr){std::cout << ' ' << *itr;}std::cout << '\n';
}int main()
{Vector<int> a;Vector<int> first;                   // empty vector of intscheck(first.empty() == true);check(first.size() == 0);Vector<int> second(4, 100);                       // four ints with value 100check(second.empty() == false);check(second.size() == 4);check(*second.begin() == 100);Vector<int> fourth(second);                       // a copy of thirdcheck(fourth.size() == second.size());int myints[] = { 16,2,77,29 };Vector<int> fifth(myints, myints + sizeof(myints) / sizeof(int));check(fifth.empty() == false);check(fifth[0] == 16);check(fifth[3] == 29);check(fifth.size() == sizeof(myints) / sizeof(int));print(fifth, "fifth");//The contents of fifth are:16 2 77 29 fifth.push_back(30);check(fifth[4] == 30);check(fifth.size() == 5);print(fifth, "fifth");//The contents of fifth are:16 2 77 29 30 check(fifth.size() == sizeof(myints) / sizeof(int) + 1);first = fifth = fifth;print(first, "first");//The contents of first are:16 2 77 29 30 check(first.empty() == false && first.size() == fifth.size());print_itr(fifth, "fifth");//The contents of fifth are:16 2 77 29 30 print_const_itr(fifth, "fifth");//The contents of fifth are:16 2 77 29 30 std::sort(fifth.begin(), fifth.end());std::cout << "fifith after sort:" << std::endl;print_const_itr(fifth, "fifth");//The contents of fifth are:16 2 77 29 30 Vector<int> a1(myints, myints + sizeof(myints) / sizeof(int));{Vector<int> b(a1);b.push_back(2);check(b[4] == 2);auto result = (b == Vector<int>{ 16, 2, 77, 29, 2});check(result);//iteratorcheck(b.begin() + b.size() == b.end());auto begin = b.begin();auto itr = b.begin() + 1;check(*begin == 16);check(*itr == 2);}{Vector<int> b{ 1,3,5,7 };b.push_back(9);}{Vector<int> c;for (auto i : c){std::cout << i << " ";}c = a1;for (auto i : c){std::cout << i << " ";}std::cout << std::endl;}check(a1.size() == sizeof(myints) / sizeof(int));{Vector<int> c;c = fifth;c[0] = 1;check(c[0] == 1);}
}

预期输出

line:42 Pass
line:43 Pass
Vector(count, value)
line:45 Pass
line:46 Pass
line:47 Pass
line:49 Pass
Vector(T* start, T* end)
line:53 Pass
line:54 Pass
line:55 Pass
line:56 Pass
The contents of fifth are: 16 2 77 29
line:59 Pass
line:60 Pass
The contents of fifth are: 16 2 77 29 30
line:62 Pass
Vector::operator=
Vector::operator=
The contents of first are: 16 2 77 29 30
line:65 Pass
The contents of fifth are: 16 2 77 29 30
The contents of fifth are: 16 2 77 29 30
fifith after sort:
The contents of fifth are: 2 16 29 30 77
Vector(T* start, T* end)
line:75 Pass
line:77 Pass
line:80 Pass
line:83 Pass
line:84 Pass
Vector::operator=
16 2 77 29 
line:103 Pass
Vector::operator=
line:108 Pass
Memory leak report: 
No memory leak.