【面试题001-补充】C++ MyString类的封装

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#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_

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#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;

}

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#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;

}

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.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)

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c

abAdefg

xyzabc

xxxyyy

aaaxxxsdfadfaxxxx

xxxyyy

xxxyyy

adf

adf