【面试题一的补充】C++ MyString类的封装

一，C++ MyString类的封装

String.h:

#ifndef _STRING_H_
#define _STRING_H_
#include <iostream>
using namespace std;

class String
{
public:
	String(const char* str="");
	String(const String& other);
	String& operator=(const String& other);
	String& operator=(const char* str);

	bool operator!() const;
	char& operator[](unsigned int index);
	const char& operator[](unsigned int index) const;

	friend String operator+(const String& s1, const String& s2);
	String& operator+=(const String& other);

	friend ostream& operator<<(ostream& os, const String& str);
	friend istream& operator>>(istream& is, String& str);
	~String(void);

	void Display() const;

private:
	String& Assign(const char* str);
	char* AllocAndCpy(const char* str);
	char* str_;
};

#endif // _STRING_H_

String.cpp:

#pragma warning(disable:4996)
#include "String.h"
#include <string.h>
//#include <iostream>
//using namespace std;

String::String(const char* str)
{
	str_ = AllocAndCpy(str);
}

String::String(const String& other)
{
	str_ = AllocAndCpy(other.str_);
}

String& String::operator=(const String& other)
{
	if (this == &other)
		return *this;

	return Assign(other.str_);
}

String& String::operator=(const char* str)
{
	return Assign(str);
}

String& String::Assign(const char* str)
{
	delete[] str_;
	str_ = AllocAndCpy(str);
	return *this;
}

bool String::operator!() const
{
	return strlen(str_) != 0;
}

char& String::operator[](unsigned int index)
{
	//return str_[index];
	//non const 版本调用 const版本

	return const_cast<char&>(static_cast<const String&>(*this)[index]);
}

const char& String::operator[](unsigned int index) const
{
	return str_[index];
}

String::~String()
{
	delete[] str_;
}

char* String::AllocAndCpy(const char* str)
{
	int len = strlen(str) + 1;
	char* newstr = new char[len];
	memset(newstr, 0, len);
	strcpy(newstr, str);

	return newstr;
}

void String::Display() const
{
	cout<<str_<<endl;
}

String operator+(const String& s1, const String& s2)
{
	//int len = strlen(s1.str_) + strlen(s2.str_) + 1;
	//char* newstr = new char[len];
	//memset(newstr, 0, len);
	//strcpy(newstr, s1.str_);
	//strcat(newstr, s2.str_);
	//
	//String tmp(newstr);
	//delete newstr;
	String str = s1;
	str += s2;
	return str;
}

String& String::operator+=(const String& other)
{
	int len = strlen(str_) + strlen(other.str_) + 1;
	char* newstr = new char[len];
	memset(newstr, 0, len);
	strcpy(newstr, str_);
	strcat(newstr, other.str_);

	delete[] str_;

	str_ = newstr;
	return *this;
}

ostream& operator<<(ostream& os, const String& str)
{
	os<<str.str_;
	return os;
}

istream& operator>>(istream& is, String& str)
{
	char tmp[1024];
	cin>>tmp;
	str = tmp;
	return is;
}

main.cpp:

#include "String.h"
#include <iostream>
using namespace std;

int main(void)
{
	String s1("abcdefg");

	char ch = s1[2];
	cout<<ch<<endl;

	s1[2] = 'A';
	s1.Display();

	const String s2("xyzabc");
	ch = s2[2];
	//s2[2] = 'M';
	s2.Display();

	String s3 = "xxx";
	String s4 = "yyy";

	String s5 = s3 + s4;
	s5.Display();

	String s6 = "aaa" + s3 + "sdfadfa" + "xxxx";
	s6.Display();

	s3+=s4;
	s3.Display();

	cout<<s3<<endl;

	String s7;
	cin>>s7;
	cout<<s7<<endl;

	return 0;
}

Makefile:

.PHONY:clean
CPP=g++
CFLAGS=-Wall -g
BIN=test
OBJS=main.o String.o
LIBS=
$(BIN):$(OBJS)
	$(CPP) $(CFLAGS) $^ -o $@ $(LIBS)
%.o:%.cpp
	$(CPP) $(CFLAGS) -c $< -o $@
clean:
	rm -f *.o $(BIN)

运行结果：

c

abAdefg

xyzabc

xxxyyy

aaaxxxsdfadfaxxxx

xxxyyy

xxxyyy

adf

adf