MyString类的实现--C++ primer plus 读书笔记

分手后的思念是犯贱 2022-08-20 14:25 115阅读 0赞

<span style="font-family: Arial, Helvetica, sans-serif; background-color: rgb(255, 255, 255);">本文实现一个简单的string类，参考自c++ primer plus这本书，源码如下：</span>

//======================================================
    // FileName: MyString.h
    // Author: sjhuangx
    // Date: 2016-03-03
    // Desc: a single string class
    //=======================================================
    
    #ifndef MYSTRING_H_INCLUDED
    #define MYSTRING_H_INCLUDED
    
    #define _CRT_SECURE_NO_WARNINGS
    #include <iostream>
    using std::ostream;
    using std::istream;
    
    
    class MyString
    {
    private:
    	char					*str;							// pointer to string
    	int					len;							// the length of string
    	static int			num_strings;			// the number of objects
    	static const int CINLIM = 80;		// the limit of cin number	
    	
    public:
    	MyString(const char* st);				// constructor from C string
    	MyString();										// default construtor
    	MyString(const MyString& st);		// copy constructor
    	~MyString();										// destructor
    	int Length() const { return len; }	// return the length of string
    
    	// overload operator methods
    	MyString& operator=(const MyString& st);
    	MyString& operator=(const char* s);
    	char& operator[](int i);
    	const char& operator[](int i) const;
    
    	// overload friend operator
    	friend bool operator<(const MyString& str1, const MyString& str2);
    	friend bool operator>(const MyString& str1, const MyString& str2);
    	friend bool operator==(const MyString& str1, const MyString& str2);
    	friend ostream& operator<<(ostream& os, const MyString& st);
    	friend istream& operator>>(istream& is, MyString& st);
    
    	// static function
    	int HowMany();
    };
    
    #endif // MYSTRING_H_INCLUDED

以下是类的实现部分：

//======================================================
    // FileName: MyString.h
    // Author: sjhuangx
    // Date: 2016-03-03
    // Desc: a single string class
    //=======================================================
    
    
    #include "MyString.h"
    
    // static member
    int MyString::num_strings = 0;
    
    // static function
    int MyString::HowMany()
    {
    	return num_strings;
    }
    
    // class methods
    MyString::MyString(const char * s) // construct string from C string
    {
    	if (s == NULL)
    	{
    		len = 0;							// set size
    		str = new char[1];			// allot storage
    		str[0] = '\0';					// initialize pointer
    	}
    	else
    	{
    		len = std::strlen(s);				// set size
    		str = new char[len + 1];		// allot storage
    		std::strcpy(str, s);					// initialize pointer				
    	}
    	num_strings++;	// set object count
    }
    
    // default constructor
    MyString::MyString()
    {
    	len = 0;
    	str = new char[1];
    	str[0] = '\0';					// default string
    	num_strings++;
    }
    
    // necessary destructor
    MyString::~MyString()
    {
    	--num_strings;	// update static member
    	delete[] str;		// delete the space
    	len = 0;				// reset len
    }
    
    // copy constructor
    MyString::MyString(const MyString& st)
    {
    	len = st.len;							// same length
    	str = new char[len + 1];		// allot space
    	std::strcpy(str, st.str);			// copy date to new location
    	++num_strings;					// handle static member update
    }
    
    //============ overload operator methods =============
    
    // assign String to String
    MyString& MyString::operator=(const MyString& st)
    {
    	if (this == &st)
    	{
    		return *this;
    	}
    
    	delete[] str;
    	len = st.len;
    	str = new char[len + 1];
    	std::strcpy(str, st.str);
    	return *this;
    }
    
    // assign a C string to MyString
    MyString& MyString::operator=(const char* st)
    {
    	if (st == NULL)
    	{
    		return *this;
    	}
    	delete[] str;
    	len = std::strlen(st);
    	str = new char[len + 1];
    	std::strcpy(str, st);
    	return *this;
    }
    
    // read-write char access for non-const Strings
    char& MyString::operator[](int i)
    {
    	if (i > len)	// if i large than length of string, then return the last of string
    	{
    		i = len;
    	}
    	if (i < 0)	// if i less then 0, than return the first of string
    	{
    		i = 0;
    	}
    	return str[i];
    }
    
    // read-only char access for const String
    const char& MyString::operator[](int i) const
    {
    	if (i > len)	// if i large than length of string, then return the last of string
    	{
    		i = len;
    	}
    	if (i < 0)	// if i less then 0, than return the first of string
    	{
    		i = 0;
    	}
    	return str[i];
    }
    
    //============== overload friend operators ===============
    
    // overload less operator
    bool operator<(const MyString& str1, const MyString& str2)
    {
    	return (std::strcmp(str1.str, str2.str) < 0);
    }
    
    bool operator>(const MyString& str1, const MyString& str2)
    {
    	return (std::strcmp(str1.str, str2.str) > 0);
    }
    
    bool operator==(const MyString& str1, const MyString& str2)
    {
    	return (std::strcmp(str1.str, str2.str) == 0);
    }
    
    // simple string outpout
    ostream& operator<<(ostream& os, const MyString& st)
    {
    	os << st.str;
    	return os;
    }
    
    // simple string input
    istream& operator>>(istream& is, MyString& st)
    {
    	char temp[MyString::CINLIM];
    	is.get(temp, MyString::CINLIM);
    	if (is)
    	{
    		st = temp;
    	}
    	while (is && is.get() != '\n')
    	{
    		continue;
    	}
    	return is;
    }

简单测试如下：

#include "MyString.h"
    using namespace std;
    
    int main(int argc, char** argv)
    {
    	MyString mystr;
    	mystr = "hello world";
    	cout << mystr << endl;
    
    	system("pause");
    	return 0;
    }

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