C++11的新特性：右值引用

先看代码

#include "pch.h"

#include <iostream>

#include <string>

using namespace std;

template <typename elemType>

class MyArray

{

public:

	MyArray(int capacity);

	MyArray(const MyArray<elemType>& arr);

	~MyArray();

	elemType& operator[](int index);

	MyArray<elemType> operator=(const MyArray<elemType>& arr);

	void PushBack(elemType& data);

	int GetSize() const { return this->mSize; }

	//void PushBack(T&& data);

private:

	int mCapacity;

	int mSize;

	elemType *pAddr;

};

template <typename elemType>

MyArray<elemType>::MyArray(int capacity)

{

	this->mCapacity = capacity;

	this->mSize = 0;

	this->pAddr = new elemType[this->mCapacity];

}

template <typename elemType>

elemType& MyArray<elemType>::operator[](int index)

{

	if (index > this->mCapacity || index < 0)

	{

		//异常

	}

	else

	{

		return *(this->pAddr + index);

	}

}

template<typename elemType>

void MyArray<elemType>::PushBack(elemType& data)

{

	if (this->mSize >= this->mCapacity)

	{

		//异常

		return;

	}

	else

	{

		*(this->pAddr + this->mSize) = data;

		this->mSize++;

	}

}

template<typename elemType>

MyArray<elemType>::MyArray(const MyArray<elemType>& arr)

{

	this->mCapacity = arr.mCapacity;

	this->mSize = arr.mSize;

	//申请内存空间

	this->pAddr = new elemType[this->mCapacity];

	//数据拷贝

	for (int ix = 0; ix < this->mSize; ++ix)

	{

		this->pAddr[ix] = arr.pAddr[ix];

	}

}

template<typename elemType>

MyArray<elemType>::~MyArray()

{

	if (this->pAddr != NULL)

	{

		delete[] this->pAddr;

	}

}

template<typename elemType>

MyArray<elemType> MyArray<elemType>::operator=(const MyArray<elemType>& arr)

{

	if (this->pAddr != NULL)

	{

		delete[] this->pAddr;

	}

	this->mCapacity = arr.mCapacity;

	this->mSize = arr.mSize;

	//申请内存空间

	this->pAddr = new elemType[this->mCapacity];

	//数据拷贝

	for (int ix = 0; ix < this->mSize; ++ix)

	{

		this->pAddr[ix] = arr.pAddr[ix];

	}

	return *this;

}

void test01()

{

	MyArray<int> marray(20);

	int a = 10;

	int b = 20;

	int c = 30;

	int d = 40;

	marray.PushBack(a);

	marray.PushBack(b);

	marray.PushBack(c);

	marray.PushBack(d);

	marray.PushBack(100);

	marray.PushBack(200);

	for (int ix = 0; ix < marray.GetSize(); ++ix)

	{

		cout << marray[ix] << " ";

	}

}

int main()

{

	test01();

	return 0;

}

代码模拟了STL中的array容器，编译代码，报错

报错的代码为

	marray.PushBack(100);

	marray.PushBack(200);

PushBack()的实现如下

template<typename elemType>

void MyArray<elemType>::PushBack(elemType& data)

{

	if (this->mSize >= this->mCapacity)

	{

		//异常

		return;

	}

	else

	{

		*(this->pAddr + this->mSize) = data;

		this->mSize++;

	}

}

其参数为引用，不能对右值取引用，也就是说

int i = &42;

这行代码是错误的。

	//不能对右值取引用

	//左值 可以在多行使用

	//右值 即临时变量，只能在当前行使用

	marray.PushBack(100);

	marray.PushBack(200);

解决办法：重载PushBack()函数

template<typename elemType>

void MyArray<elemType>::PushBack(elemType && data)

{

	if (this->mSize >= this->mCapacity)

	{

		//异常

		return;

	}

	else

	{

		*(this->pAddr + this->mSize) = data;

		this->mSize++;

	}

}

另：

在VS2017开发环境中，将PushBack()的函数实现如下

void PushBack(const elemType& data);    //类内声明

template<typename elemType>  //类外实现

void MyArray<elemType>::PushBack(const elemType& data)

{

	if (this->mSize >= this->mCapacity)

	{

		//异常

		return;

	}

	else

	{

		*(this->pAddr + this->mSize) = data;

		this->mSize++;

	}

}

这样在使用PushBack()时，编译不会报错

	marray.PushBack(100);

	marray.PushBack(200);

但在Linux下，gcc版本为4.4.6，即便是写为

void PushBack(const elemType& data);    //类内声明

编译器仍旧会报错。

巴特西

C++11的新特性：右值引用

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