string_自定义

string类的基本操作

// Study.cpp: 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <iostream>
#include <vector>
#include <unordered_map>
#include <unordered_set>
#include <queue>
#include <string>
#include <algorithm>
#include <sstream>
using namespace std;

class myString;
class myString {
	friend ostream& operator<<(ostream& out, const myString& ss);
public:
	//普通构造函数
	myString(const char* word=nullptr)
	{
		if (word == nullptr)
		{
			p = new char;
			//需要判断是否成功分配内存  p == nullptr ??
			if (p == nullptr)
			{
				cout << "申请内存失败 " << endl;
				return;
			}
			*p = '\0';
			length = 0;
		}
		else
		{
			length = strlen(word);
			p = new char[length+1];
			//需要判断是否成功分配内存  p == nullptr ??
			if (p == nullptr)
			{
				cout << "申请内存失败 " << endl;
				return;
			}
			strcpy(p, word);
		}


	}
	//拷贝构造函数
	myString(const myString & ss)
	{
		p = new char [ss.length + 1];
		//需要判断是否成功分配内存  p == nullptr ??
		if (p == nullptr)
		{
			cout << "申请内存失败 " << endl;
			return;
		}
		strcpy(p, ss.p);
		length = ss.length;
	}
	myString& operator=(const myString &ss)
	{
		//检查自赋值
		if (this == &ss)
			return *this;

		//删除原来的内存资源
		delete []p;

		length = ss.length;
		p = new char[length + 1];
		//需要判断是否成功分配内存  p == nullptr ??
		if (p == nullptr)
		{
			cout << "申请内存失败 " << endl;
			return *this;
		}
		strcpy(p, ss.p);
		return *this;
	}

	~myString()
	{
		delete []p;
	}
private:
	char* p;
	int length;
};
ostream& operator<<(ostream& out, const myString& ss)
{
	out << (ss.p);
	return out;
}


int main()
{

	myString a("Hello World !");
	myString b("Let's go ");
	cout << "a : "<< a << endl;
	cout << "b : " << b << endl;
	myString c(b);
	cout << "c : " << c << endl;
	a = b;
	cout << "a : " << a << endl;

	string x("X");
	cout << x.substr(0, 2) << endl;
	system("pause");
	return 0;
}