Question

背景

我试图自己实现std :: vector。现在，我只有它的专用版本，它有MyStruct实例作为元素。元素类型具有辅助输出，如信号的构造方式（复制，移动，值，默认ctor）。我添加了运算符的重载＆lt;＆lt;使调试更方便。我正在使用Microsoft Visual Studio 2015更新1.

问题：

首先，似乎emplace_back调用没有做它应该做的事情。试图输出返回元素它输出垃圾。另外，当退出main（）的范围时，有错误说程序试图写入堆外的内存。添加了消息框的图像。

修改

推回几乎相同的增加容量的实现工作。还添加了实现和声明。

以下是代码：

的main.cpp

#include "MyStruct.h"
#include <iostream>
#include <cstdlib>
#include "vector.h"

int main()
{
MyStruct ms(0);
Vector v;
v.emplace_back(2);

std::cout << v.back() << "\n";

std::system("pause");
}

vector.h

#pragma once
#include "MyStruct.h"

class Vector
{
    size_t mcapacity;
    MyStruct* mdata;
    size_t msize;
public:
    Vector();

    MyStruct& back();

    void push_back(const MyStruct& ms);

    template<typename ... ArgsType>
    void emplace_back(ArgsType ... args)
    {
        if (mcapacity == msize && msize == 0)
        {
            mdata = (MyStruct*)operator new[](sizeof(MyStruct));
            mcapacity++;
        }
        else if (mcapacity == msize)
        {
            MyStruct* tempdata = (MyStruct*)operator new[](sizeof(MyStruct) * mcapacity * 2);
            for (size_t i = 0; i < msize; i++)
            {
                new (tempdata + i) MyStruct(*(mdata + i));
            }
            mdata = tempdata;
            mcapacity *= 2;
        }
        new (mdata + msize) MyStruct(std::forward<ArgsType...>(args...));
        msize++;
    }

    ~Vector();
};

vector.cpp

#include "vector.h"
#include "MyStruct.h"
#include <iostream>

Vector::Vector() :
    mdata(nullptr), 
    msize(0), 
    mcapacity(0)
{

}

MyStruct& Vector::back()
{
    return *(mdata + msize - 1);
}

void Vector::push_back(const MyStruct& ms)
{
    if (mcapacity == msize && msize == 0)
    {
        mdata = (MyStruct*)operator new[](sizeof(MyStruct));
        mcapacity++;
    }
    else if (mcapacity == msize)
    {
        MyStruct* tempdata = (MyStruct*)operator new[](sizeof(MyStruct) * mcapacity * 2);
        for (size_t i = 0; i < msize; i++)
        {
            new (tempdata + i) MyStruct(*(mdata + i));
        }
        mdata = tempdata;
        mcapacity *= 2;
    }

    new (mdata + msize) MyStruct(ms);
    msize++;
}

Vector::~Vector()
{
    for (size_t i = 0; i < msize; i++)
    {
        (mdata + i)->~MyStruct();
    }

    operator delete[](mdata);//next statement to execute
}

以下是错误消息框：

输出：

I'm constructed using value constructor
I'm constructed using value constructor
I'm printing the number -33686019!

这是MyStruct标头和实现，但我认为没有任何函数抛出任何异常或调用未定义的行为。添加了所有构造函数，因为我不确定在调用v.back（）时实际调用了哪个构造函数。认为编译器可能会进行一些优化。但根据输出，价值ctor被称为。

MyStruct.h

#pragma once
#include <iosfwd>

class MyStruct
{
    int x;
public:
    MyStruct();
    MyStruct(int x_);

    MyStruct(const MyStruct& other);

    MyStruct(MyStruct&& other) noexcept;

    void print(std::ostream& os) const;

    ~MyStruct();
};

std::ostream& operator<<(std::ostream& os, const MyStruct& ms);

MyStruct.cpp

#include "MyStruct.h"
#include <iostream>

MyStruct::MyStruct():
    x(0)
{
    std::cout << "I'm created using default constructor" << "\n";
}

MyStruct::MyStruct(MyStruct&& other) noexcept :
    x(other.x)
{
    std::cout << "I'm created using move constructor" << "\n";
}

MyStruct::MyStruct(const MyStruct& other):
    x(other.x)
{
    std::cout << "I'm created using copy constructor" << "\n";
}

MyStruct::~MyStruct()
{
    std::cout << "I'm destructed" << "\n";
}

void MyStruct::print(std::ostream& os) const
{
    os << "I'm printing the number " << x << "!\n";
}

std::ostream& operator<<(std::ostream& os, const MyStruct& ms)
{
    ms.print(os);
    return os;
}

MyStruct::MyStruct(int x_) :
    x(x_)
{
    std::cout << "I'm constructed using value constructor" << "\n";
}

实现我自己的vector :: emplace_back

0 个答案: