C++ string类的实现

string类的简单实现

/*
* String类的简单实现
* Build 20160701
* Author: LonelyEnvoy
* Copyright (c) 2015-2016
* All Rights Reserved.
*/

#define MAX_LENGTH 50
#define NULL 0

#include <iostream>
using std::ostream;
using std::istream;
using std::cout;
using std::endl;

class String
{
public:
String(const char* s = NULL);
String(const String &obj);
~String();
void set(char* s);
char* get() const;
void print() const;
int size() const;

static int strlen(const char* s);
static char* strcat(char* s1, const char* s2);
static char* strcpy(char* s1, const char* s2);

String operator+(String& obj2);
String& operator=(String& obj2);
String& operator=(const char* s2);
String& operator+=(String& obj2);
char& operator[](unsigned n);
friend ostream & operator << (ostream & os, const String & obj);
friend istream & operator >> (istream & is, String & obj);

private:
char* str;
};

String::String(const char * s)
{
if (s == NULL)
str = NULL;
else
{
str = new char[strlen(s) + 1];
strcpy(str, s);
}
}

String::String(const String & obj)
{
if (obj.str == NULL)
str = NULL;
else
{
str = new char[strlen(obj.str) + 1];
strcpy(str, obj.str);
}
}

String::~String()
{
if (str == NULL)
return;
delete[]str;
}

void String::set(char * s)
{
if (s == NULL)
return;
if (str != NULL)
delete[]str;

str = new char[strlen(s) + 1];

int i;
for (i = 0; i < strlen(s); i++)
str[i] = s[i];
s[i] = '\0';
}

char * String::get() const
{
return str;
}

void String::print() const
{
for (int i = 0; i < strlen(str); i++)
cout << str[i];
cout << endl;
}

int String::size() const
{
return strlen(str);
}

int String::strlen(const char * s)
{
if (s == NULL)
return 0;
int i = 0;
while (s[++i] != '\0');
return i;
}

char * String::strcat(char * s1, const char * s2)
{
// s1 must have enough space for storage
if (s1 == NULL || s2 == NULL)
return NULL;
int i, j;
for (i = strlen(s1), j = 0; j < strlen(s2); i++, j++)
s1[i] = s2[j];
s1[i] = '\0';
return s1;
}

char * String::strcpy(char * s1, const char * s2)
{
// s1 must have enough space for storage
if (s1 == NULL || s2 == NULL)
return NULL;
int i;
for (i = 0; i < strlen(s2); i++)
s1[i] = s2[i];
s1[i] = '\0';
return s1;
}

String String::operator+(String & obj2)
{
String s;
if (str == NULL || obj2.str == NULL)
return String();
else if (str == NULL)
s = obj2;
else if (obj2.str == NULL)
s = *this;
else
{
s.str = new char[strlen(str) + strlen(obj2.str) + 1];
strcpy(s.str, str);
strcat(s.str, obj2.str);
}
return s;
}

String & String::operator=(String & obj2)
{
if (this != &obj2)
{
delete[]str;
if (obj2.str == NULL)
str = NULL;
else
{
str = new char[strlen(obj2.str) + 1];
strcpy(str, obj2.str);
}
}
return obj2;
}

String & String::operator=(const char * s2)
{
String temp(s2);
operator=(temp);
return temp;
}

String & String::operator+=(String & obj2)
{
operator=(operator+(obj2));
return obj2;
}

char & String::operator[](unsigned n)
{
if (n >= 0 && n < (unsigned)size())
return str
;
throw 1; // 越界抛出异常
}

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

istream & operator>>(istream & is, String & obj)
{
char temp[MAX_LENGTH];
is >> temp;
obj = temp;
return is;
}