string2.cpp

我学习C++ Primer Plus过程中写下的课后作业的编程代码

// string2.cpp -- String class methods
#include <cstring>		// string.h for some
#include "String2.h"	// include <iostream>
using std::cin;
using std::cout;

const int String::CINLIM = 80;
String::String()
{
	len = 0;
	str = new char[1];
	str[0] = '\0';		    	// default string
}

// class methods
String::String(const char * s)	// construct String from C string
{
	len = strlen(s);		    // set size
	str = new char[len+1];   	// allot storage
	strcpy(str,s);
}


String::String(const String & st)	// copy constructor
{
	len = st.len;			
	str = new char[len+1];
	strcpy(str,st.str);		
}

String::~String()			// necessary destructor
{
	delete[]str;
}

void String::stringlow()	// tolower
{
	char * str_temp = str;
	while(*str_temp)
	{
		*str_temp = tolower(*str_temp);
		str_temp++;
	}
}

void String::stringup()		// toupper
{
	char * str_temp = str;
	while(*str_temp)
	{
		*str_temp = toupper(*str_temp);
		str_temp++;
	}
}

int String::has(const char & c)const	// count how many 'c' in string
{
	int n = 0;
	char * str_temp = str;
	while(*str_temp)
	{
		if(c == *str_temp)
			n++;
		str_temp++;
	}
	return n;
}

// overloaded operator methods
// assign a String to a String
String & String::operator= (const String & st)
{
	if (this == &st)
		return  *this;
	delete []str;
	len = st.len;
	str = new char[len+1];
	strcpy (str, st.str);
	return *this;
}

String & String::operator = (const char * s)
{
	delete []str;
	len = strlen(s);
	str = new char[len+1];
	strcpy(str,s);
	return *this;
}

// read-write char access for non-const String
char & String::operator [] (int i)
{
	return str[i];
}

// read-only char access for const String
const char & String::operator [] (int i)const
{
	return str[i];
}

String String::operator + (const String & st)
{
	String temp;
	temp.len = len + st.len;
	delete []temp.str;
	temp.str = new char[temp.len+1];
	strcat(temp.str,str);
	strcat(temp.str,st.str);
	return temp;
}
String String::operator + (const char * st)
{
	String temp;
	temp.len = len + strlen(st);
	delete []temp.str;
	temp.str = new char[temp.len+1];
	strcat(temp.str,str);
	strcat(temp.str,st);
	return temp;
}	


// overload operator friends
bool operator< (const String &st1, const String &st2)
{
	return ( strcmp(st1.str,st2.str) < 0 );
}

bool operator> (const String &st1, const String &st2)
{
	return st2.str < st1.str;
}

bool operator == (const String &st1, const String &st2)
{
	return (strcmp(st1.str,st2.str) == 0);
}

// simple String output
ostream & operator<< (ostream & os, const String &st)
{
	os<<st.str;
	return os;
}

// quick and dirty String input
istream & operator>> (istream & is, String & st)
{
	char temp[String::CINLIM];
	if (is)
		st = temp;
	while (is && is.get() != '\n')	// 超过CINLIM则从输入流中去除
		continue;
	return is;
}

String operator + (const char * st1, const String & st2) // 主要是重载 + 操作符不明白
{
	String temp;
	temp.len = strlen(st1) + st2.len;
	delete []temp.str;
	temp.str = new char[temp.len+1];
	strcat(temp.str,st1);
	strcat(temp.str,st2.str);
	return temp;
}