C++：默认成员函数

素颜马尾好姑娘i 2022-03-18 05:52 202阅读 0赞

在C++11前，类中默认的成员函数有4个，分别是：

> 1.Default constructor  
> 2.Copy constructor  
> 3.Copy assignment operator  
> 4.Destructor

C++11之后，又新增了两个：

> 5.Move Constructor  
> 6.Move Assignment Operator

下面举一个字符串类的例子，来说明这6个函数一般是如何实现方式的：

// tstring.h
    
    class TString {
    
    private:
    
    	char* m_data = nullptr;
    
    	int m_length = 0;
    
    public:
    
    	// Default constructor
    	TString();
    
    	// Copy constructor
    	TString(const TString& srcStr);
    
    	// Copy assignment operator
    	TString& operator=(const TString& srcStr);
    
    	// Destructor
    	~TString();
    
    	// Move Constructor
    	TString(TString&& srcStr);
    
    	//  Move Assignment Operator
    	TString& operator=(TString&& srcStr);
    
    	//------------------------------------------
    	// Self-Defined constructor
    	TString(const char* src);
    
    	int length();
    
    	static int strlen(const char* src);
    
    	static char* strcpy(char* dst, const char* src);
    };

//tsring.cpp
    
    #include "tsring.h"
    #include <cassert>
    
    int TString::strlen(const char* src) {
    	int len = 0;
    
    	if (src == nullptr) {
    		len = 0;
    	}
    	else {
    		const char *temp = src;
    
    		while (*temp++ != '\0') {
    			len++;
    		}
    	}
    
    	return len;
    };
    
    char* TString::strcpy(char* dst, const char* src) {
    	assert(dst != nullptr && src != nullptr);
    
    	char* temp = dst;
    	while ((*temp = *src) != '\0') {
    		temp++;
    		src++;
    	};
    
    	return temp;
    };
    
    TString::TString(const char* src) {
    	if (src != nullptr) {
    		char *temp = new char[strlen(src) + 1];
    		assert(nullptr != temp);
    		m_data = strcpy(temp, src);
    	}
    	else {
    		m_data = new char[1];
    		assert(nullptr != m_data);
    		*m_data = '\0';
    	}
    
    	m_length = strlen(m_data);
    };
    
    int TString::length() {
    	return m_length;
    };
    
    //------------------------------------------
    TString::TString() {
    	m_data = new char[1];
    	assert(nullptr != m_data);
    	*m_data = '\0';
    };
    
    TString::TString(const TString& srcStr) {
    	char *temp = new char[srcStr.m_length + 1];
    	assert(nullptr != temp);
    	strcpy(temp, srcStr.m_data);
    
    	m_data = temp;
    	m_length = srcStr.m_length;
    };
    
    TString& TString::operator=(const TString& srcStr) {
    	if (this == &srcStr) {
    		return *this;
    	}
    
    	char *temp = new char[srcStr.m_length + 1];
    	assert(nullptr != temp);
    	strcpy(temp, srcStr.m_data);
    
    	delete[] m_data;
    	m_data = temp;
    	m_length = srcStr.m_length;
    
    	return *this;
    };
    
    TString::~TString() {
    	delete[] m_data;
    
    	m_data = nullptr;
    	m_length = 0;
    };
    
    TString::TString(TString&& srcStr) {
    	m_data = srcStr.m_data;
    	m_length = srcStr.m_length;
    
    	srcStr.m_data = nullptr;
    	srcStr.m_length = 0;
    };
    
    TString& TString::operator=(TString&& srcStr) {
    	if (this == &srcStr) {
    		return *this;
    	}
    
    	m_data = srcStr.m_data;
    	m_length = srcStr.m_length;
    
    	srcStr.m_data = nullptr;
    	srcStr.m_length = 0;
    
    	return *this;
    };

另外，需要说明的是，不存在如下形式的构造函数，因为它会造成无限递归调用，最终导致栈溢出

TString(TString srcStr);

参考文档  
[Constructors (C++)][Constructors _C]  
[C++ Rvalue References Explained][C_ Rvalue References Explained]  
[详解C++右值引用][C]  
[Constructors in C++11][Constructors in C_11]

[Constructors _C]: https://docs.microsoft.com/en-us/cpp/cpp/constructors-cpp?view=vs-2017
[C_ Rvalue References Explained]: http://thbecker.net/articles/rvalue_references/section_01.html
[C]: https://blog.csdn.net/renwotao2009/article/details/46335859
[Constructors in C_11]: https://www.developerfusion.com/article/133063/constructors-in-c11/