自己实现C++String类

àì夳堔傛蜴生んèń 2022-11-15 11:53 116阅读 0赞

## 简单String类功能实现 ##

一般是要求实现构造函数、拷贝构造函数、赋值函数、析构函数这几个非常重要的部分。因为String里涉及动态内存的管理，默认的拷贝构造函数在运行时只会进行浅复制，即只复制内存区域的指针，会造成两个对象指向同一块内存区域的现象。如果一个对象销毁或改变了该内存区域，会造成另一个对象运行或者逻辑上出错。这时就要求程序员自己实现这些函数进行深复制，即不止复制指针，需要连同内存的内容一起复制。

具体代码如下：

/****************** Author : 杨永利 data : 2020-06-28 *******************/
    #include <string.h>
    #include <assert.h>
    #include <iostream>
    
    using namespace std;
    
    class String
    { 
    public:
    	String(const char *str = NULL);	//通用构造函数
    	String(const String &str);		//拷贝构造函数(深赋值)
    	~String();						//析构函数
    
    	String operator+(const String &str) const;	//重载+
    	String& operator=(const String &str);		//重载=
    	String& operator+=(const String &str);		//重载+=
    	bool operator==(const String &str) const;	//重载==
    	char& operator[](int n) const{ assert(n <= length - 1); return data[n]; }	//重载[](内联函数)
    
    	size_t size() const{  return length; }		//长度接口(内联函数)
    	const char* c_str() const{  return data; }	//数据接口(内联函数)
    
    	friend istream& operator>>(istream &is, String &str);//输入
    	friend ostream& operator<<(ostream &os, String &str);//输出
    
    private:
    	char *data;		//字符串
    	size_t length;	//长度
    };
    
    String::String(const char *str)
    { 
    	if(str == NULL)
    	{ 
    		length = 0;
    		data = new char[1];
    		*data = '\0';
    	}else{ 
    		length = strlen(str);
    		data = new char[length + 1];
    		strcpy(data, str);
    	}
    }
    
    String::String(const String &str)
    { 
    	length = str.size();
    	data = new char[length + 1];
    	strcpy(data, str.c_str());
    }
    
    String::~String()
    { 
    	delete []data;
    	length = 0;
    }
    
    String String::operator+(const String &str) const
    { 
    	String newString;
    	newString.length = length + str.size();
    	newString.data = new char[newString.length + 1];
    	strcpy(newString.data, data);
    	strcat(newString.data, str.data);
    	return newString;
    }
    
    String& String::operator=(const String &str)
    { 
    	if(this == &str)
    	{ 
    		return *this;
    	}
    	
    	delete []data;
    	length = str.size();
    	data = new char[length + 1];
    	
    	strcpy(data, str.c_str());
    	
    	return *this;
    }
    
    String& String::operator+=(const String &str)
    { 
    	if(str.size() == 0)
    	{ 
    		return *this;
    	}
    	
    	length += str.size();
    	char *t_data = new char[length + 2];
    	
    	strcpy(t_data, data);
    	strcat(t_data, str.c_str());
    	
    	delete []data;
    	data = t_data;
    	
    	return *this;
    }
    
    bool String::operator==(const String &str) const
    { 
    	if(length == str.size() && !strcmp(data, str.c_str()))
    	{ 
    		return true;
    	}
    	
    	return false;
    }
    
    istream& operator >>(istream &is, String &str)
    { 
    	char temp[1024];
    	is >> temp;
    	str.length = strlen(temp);
    	str.data = new char[str.length + 1];
    	strcpy(str.data, temp);
    	
    	return is;
    }
    
    ostream& operator<<(ostream &os, String &str)
    { 
    	os << str.data;
    	
    	return os;
    }
    
    int main()
    { 
    	String s;	
    	cin >> s;	
    	cout << s << ": " << s.size() << endl;
    
    	char a[] = "Hello", b[] = "World!";
    	String s1(a), s2(b);	
    	cout << s1 << " + " << s2 << " = " << s1 + s2 << endl;
    
    	String s3 = s1 + s2;
    	if (s1 == s3)	cout << "First: s1 == s3" << endl;
    	s1 += s2;
    	if (true == (s1 == s3))	cout << "Second: s1 == s3" << endl;
    	
    	cout<<s1[3]<<endl;
    	
    	return 0;
    }

**运行结果如下：**  
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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTUyNTI3Mg_size_16_color_FFFFFF_t_70]: /images/20221022/0dcad568c46c431296480d088ad4b264.png