C++学习(13)

  1 //字符串类的设计
  2 //1.字符串类String能与C语言的字符串兼容使用
  3 //2.重载逻辑等于运算符(==)
  4 //3.字符串操作包括取字符串长度和取子串
  5 #include<string.h>
  6 #include<iostream.h>
  7 #include<stdlib.h>
  8 class String{
  9     private:
 10         char *str;
 11         int size;
 12     public:
 13 //        String();
 14         String(char *s="");
 15         String(const String &s);
 16         ~String();
 17 
 18         int Length()const;
 19         String SubStr(int pos,int length);
 20 
 21         String &operator=(const String &s);
 22         String &operator=(char *s);
 23 
 24         int operator==(const String &s)const;
 25         int operator==(char *s)const;
 26 
 27         friend int operator==(char *strL,const String &strR);
 28 };
 29 
 30 //String::String(){}
 31 String::String(char *s){
 32     this->size=strlen(s)+1;
 33     str=new char[size];
 34     strcpy(str,s);
 35 }
 36 
 37 String::String(const String &s){
 38     this->size=s.size;    
 39     str=new char[size];
 40     if(str==NULL){
 41         exit(0);
 42     }
 43     for(int i=0;i<size;i++){
 44         this->str[i]=s.str[i];
 45     }
 46 }
 47 
 48 String::~String(){
 49     delete []this->str;
 50 }
 51 
 52 
 53 int String::Length()const{
 54     return this->size;
 55 }
 56 
 57 String String::SubStr(int pos,int length){
 58     int charsLeft=size-pos-1;
 59     String temp;
 60     char *p,*q;
 61 
 62     if(pos>=size-1){
 63         return temp;
 64     }
 65     if(length>charsLeft){//长度不能超出范围
 66         length=charsLeft;
 67     }
 68     delete []temp.str;
 69     
 70     temp.str=new char[length+1];
 71 
 72     p=temp.str;
 73     q=&this->str[pos];
 74 
 75     for(int i=0;i<length;i++){
 76         *p++=*q++;
 77     }
 78         
 79     *p=NULL;
 80     temp.size=length+1;
 81     
 82     return temp;
 83 }
 84 
 85 String &String::operator =(const String &s){
 86     if(this->size!=s.size){
 87         delete []str;
 88         this->str=new char[s.size];
 89         size=s.size;
 90     }
 91     for(int i=0;i<s.size;i++){
 92         this->str[i]=s.str[i];
 93     }
 94     return *this;
 95 
 96 }
 97 
 98 String &String::operator=(char *s){
 99     int length=strlen(s);
100     if(this->size!=length){
101         delete []this->str;
102         str=new char[length+1];
103         this->size=length+1;
104     }
105     strcpy(this->str,s);
106     return *this;
107 }
108 
109 int String::operator==(const String &s)const{//String类和String类相比较
110     return strcmp(this->str,s.str)==0;
111 }
112 int String::operator==(char *s)const{//String类和C语言字符串比较
113     return strcmp(this->str,s)==0;
114 }
115 
116 int operator==(char *strL,const String &strR){//C预压字符串和String类比较
117     return strcmp(strL,strR.str)==0;
118 }
119 
120 int main(){
121 
122     String str1("Data Structure");
123     String str2("Structure");
124     String str3,str4,str5;
125 
126     cout<<str1.Length()<<endl;
127     
128     str3=str1.SubStr(5,9);
129     str4=str1.SubStr(5,9);
130     str5="Structure";
131 
132     if(str3==str4){
133         cout<<"String和String字符串比较"<<endl;
134     }
135 
136     if(str5=="Structure"){
137         cout<<"String和C语言字符串相比较"<<endl;
138     }
139     if("Strcture"==str2){
140         cout<<"C语言字符串和String相比较"<<endl;
141     }
142     return 0;
143 }