字符串类.cpp

这个代码是STRING类的声明及实现,因为我认为C++类库中的string类比较庞大,找一个函数需要很长时间,所以用一个简单明了的代替之.

/*字符串类*/
#include<iostream>
#include<cstdlib>
using namespace std;
namespace std
{                         //自定义名字空间
	const int maxlen=128;
	
	class String
	{
	private:
		int curlen;
		char *ch;
	public:
		String(char *init=" ");
		String(const String&ob);
		~String()
		{
			delete []ch;
		}
		
		//赋值运算符
		String& operator=(const String&ob);
		String& operator=(char*s);
		//关系运算符
		int operator==(const String&ob) const
		{
			return strcmp(ch,ob.ch)==0;
		}

		int operator==(char *s) const
		{
			return strcmp(ch,s)==0;
		}
		friend int operator==(char *s,const String&ob)
		{
			return strcmp(s,ob.ch)==0;
		}

		int operator!=(const String&ob) const
		{
			return strcmp(ch,ob.ch)!=0;
		}
		int operator!=(char *s) const
		{
			return strcmp(ch,s)!=0;
		}
		friend int operator!=(char *s,const String&ob)
		{
			return strcmp(s,ob.ch)!=0;
		}

		int operator<(const String&ob) const
		{
			return strcmp(ch,ob.ch)<0;
		}
		int operator<(char *s) const
		{
			return strcmp(ch,s)<0;
		}
		friend int operator<(char *s,const String&ob)
		{
			return strcmp(s,ob.ch)<0;
		}

		int operator<=(const String&ob) const
		{
			return strcmp(ch,ob.ch)<=0;
		}
		int operator<=(char *s) const
		{
			return strcmp(ch,s)<=0;
		}
		friend int operator<=(char *s,const String&ob)
		{
			return strcmp(s,ob.ch)<=0;
		}

		int operator>=(const String&ob) const
		{
			return strcmp(ch,ob.ch)>=0;
		}
		int operator>=(char *s) const
		{
			return strcmp(ch,s)>=0;
		}
		friend int operator>=(char *s,const String&ob)
		{
			return strcmp(s,ob.ch)>=0;
		}

		//串拼接运算符
		String operator+(const String& ob) const;
		String operator+(char *s) const;
		friend String operator+(char *s,const String & ob);
		String & operator+=(const String& ob);
		String & operator+=(char *s);

		//从START位置开始找字符C
		int find(char c,int start) const;
		//找字符C最后出现的位置
		int findlast(char c)const;
		//取子串	
		String substr(int index,int count) const;

		//String的下标运算
		char &operator[](int i);
		friend ostream &operator<<(ostream &ostr,const String& s);
		friend istream &operator>>(istream &istr,String& s);
		int length() const
		{
			return curlen-1;
		}
		int strempty() const 
		{
			return curlen==1;
		}
		void clear()
		{
			curlen=1;
		}
};  //类定义结束
		
String::String(const String&ob)
{
	curlen=ob.curlen;
	ch=new char[curlen];
	if(ch==NULL)
	{
		cerr<<"allocation error!\n";
			exit(1);
	}
	strcpy(ch,ob.ch);
}
String::String(char *init)
{
	curlen=strlen(init)+1;//长度包括NULL字符
	ch=new char[curlen];
	if(ch==NULL)
	{
		cerr<<"allocation error!\n";
			exit(1);
	}
	strcpy(ch,init);
}

String& String:: operator=(const String&ob)
{
	//若大小不等则删除当前串,并重新申请内存
	if(ob.curlen!=curlen)
	{
		delete[] ch;
		ch=new char[ob.curlen];
		if(ch==NULL)
		{
			cerr<<"allocation error!\n";
			exit(1);
		}
		curlen=ob.curlen;
	}
	strcpy(ch,ob.ch);
	return *this;
}

String& String::operator=(char*s)
{
	if(strlen(s)+1!=curlen)
	{
		delete []ch;
		ch=new char[strlen(s)+1];
		if(ch==NULL)
		{
			cerr<<"allocation error!\n";
			exit(1);
		}
		curlen=strlen(s)+1;
	}
	strcpy(ch,s);
	return *this;
}

String String:: operator+(const String& ob) const
{
	//在temp中建立一个长度为len的新串
	String temp;
	int len;
	//删除定义temp是产生的NULL串
	delete []temp.ch;
	//计算拼接后的串长度并且为之申请内存
	len=curlen+ob.curlen-1;//只有一个NULL结尾
	temp.ch=new char[len];
	if(temp.ch==NULL)
	{
			cerr<<"allocation error!\n";
			exit(1);
	}
	//建立新串
	temp.curlen=len;
	strcpy(temp.ch,ch);
	strcat(temp.ch,ob.ch);
	return temp;
}

String String::operator+(char *s) const
{
	String temp;
	int len;
	delete []temp.ch;
	len=curlen+strlen(s);
	temp.ch=new char[len];
	if(temp.ch==NULL)
	{
			cerr<<"allocation error!\n";
			exit(1);
	}
	temp.curlen=len;
	strcpy(temp.ch,ch);
	strcat(temp.ch,s);
	return temp;
}

String operator+(char *s,const String & ob)
{
	String temp;
	int len;
	delete []temp.ch;
	len=ob.curlen+strlen(s);
	temp.ch=new char[len];
	if(temp.ch==NULL)
	{
			cerr<<"allocation error!\n";
			exit(1);
	}
	temp.curlen=len;
	strcpy(temp.ch,s);
	strcat(temp.ch,ob.ch);
	return temp;
}


String&	String::operator+=(const String& ob)
{
	char*temp=ch;
	curlen=curlen+ob.curlen-1;
	ch=new char[curlen];
	if(ch==NULL)
	{
			cerr<<"allocation error!\n";
			exit(1);
	}
	strcpy(ch,temp);
	strcat(ch,ob.ch);
	delete []temp;
	return *this;
}
String &String::operator+=(char *s)
{
	char*temp=ch;
	curlen+=strlen(s);
	ch=new char[curlen];
	if(ch==NULL)
	{
			cerr<<"allocation error!\n";
			exit(1);
	}
	strcpy(ch,temp);
	strcat(ch,s);
	delete []temp;
	return *this;
}
int String::find(char c,int start)const
{
	int ret;
	char*p;
	p=strchr(ch+start,c);
	if(p!=NULL)
		ret=int(p-ch);
	else
		ret=-1;
	return ret;
}
int String::findlast(char c)const
{
	int ret;
	char *p;
	p=strrchr(ch,c);
	if(p!=NULL)
		ret=int(p-ch);
	else
		ret=-1;
	return ret;
}
String String::substr(int index,int count) const
{
	//从index到串尾的字符个数
	int charsleft=curlen-index-1,i;
	//建立子串temp
	String temp;
	char*p,*q;
	//若index越界.返回空串
	if(index>=curlen-1)
		return temp;
	//若count大于剩下的字符,则只用剩下的字符
	if(count>charsleft)
		count=charsleft;
	delete []temp.ch;
	temp.ch=new char[count+1];
	if(temp.ch==NULL)
	{
			cerr<<"allocation error!\n";
			exit(1);
	}
	//从ch中拷贝count个字符到 temp.ch
	for(i=0,p=temp.ch,q=&ch[index];i<count;i++)
		*p++=*q++;
	*p=0;
	temp.curlen=count+1;
	return temp;
}

char &String::operator[](int i)
{
	return ch[i];
}

	ostream &operator<<(ostream &ostr,const String& s)
	{
		cout<<s.ch;
		return ostr;
	}
	istream &operator>>(istream &istr,String& s)
	{
		s.ch=new char[maxlen];
		if(s.ch==NULL)
		{
			cerr<<"allocation error!\n";
			exit(1);
		}
		istr.getline(s.ch,maxlen,'\n');
		return istr;
	}
}//定义名字空间结束


void main()
{
	String s1("String"),s2("hello");
	String s3,s4,s5;
	char c;
	s3=s1+" "+s2;
	cout<<s3<<endl;
	cout<<"the length of s2:"<<s2.length()<<endl;
	cout<<"s2中第一个s的位置是:"<<s2.find('s',0)<<endl;
	cout<<"s2中最后一个s的位置是:"<<s2.findlast('s')<<endl;	
	cout<<"s2中第一个空格的位置是:"<<s2.find(' ',0)<<endl;
	cout<<"s2中最后一个空格的位置是:"<<s2.findlast(' ')<<endl;	
	cout<<"input s4:";
		cin>>s4;cout<<s4;
	s1="how are you?";
	for(int i=0;i<s1.length();i++)
	{
		c=s1[i];
		if(c>='A'&&c<='Z')
		{
		c+=32;
		s1[i]=c;
		}
	}
	cout<<"s1 is:"<<s1<<endl;
	s1="ABCDE";s2="BCF";
	int b=s2<s1;
	cout<<b;
	String as="0",f=s1;
	String data("300");
	data[0]='5';
	cout<<data<<" ";
	cout<<data.strempty()<<" ";
	data.clear();
	cout<<data.strempty()<<endl;
}