C++随手代码收藏 自定义实现 String 类

#include <iostream.h>#include <string.h>#include <stdlib.h>class String         //定义字符串类{      char *ss;         //字符串的首地址     int length;         //字符串长度public:     String(char *s);     //带参数的构造函数     String(){ss=0;length=0;}     //缺省的构造函数     String(String &s);             //拷贝构造函数     String& operator =(String&);//重载赋值运算符“=”(不能用友元函数重载)     String& operator =(char *);     //重载赋值运算符“=”(不能用友元函数重载)     friend String operator +(String &s1,String &s2);//可改用成员函数     friend String operator +(String &s1,char* s2);//可改用成员函数     friend String operator +(char* s1,String &s2);     String& operator +=(String&);     String& operator +=(char *);     friend int operator ==(String &s1,String &s2);//可改用成员函数     friend int operator ==(String &s1,char* s2);//可改用成员函数     friend int operator ==(char* s1,String &s2);     friend int operator >(String &s1,String &s2);//可改用成员函数int operator >(String &s2);     int operator >(char* s2);     friend int operator >(char* s1,String &s2);     char& operator [](int);     //重载下标运算符“[]”operator char*()         //类型转换函数     { return ss; }     //有了类型转换函数,某些字符串函数,如：strlen(String),strcpy(char*,String),     //strcmp(String,String)、strcmp(String,char*)、strcmp(char*,String),     //strcat(char*,String)等等不再需要重载,但strcat(String&,char*)除外     friend void strcat(String& s1,char* s2);//相当于s1+="..."     //有了上述重载函数,strcat(String& s1,String& s2)也可执行:由类型转换函数自动将s2转     //换成char*型。strcat(char *s1,...)不需要重载,只要s1有足够的存储空间就行。     friend ostream& operator <<(ostream&,String&);     friend istream& operator >>(istream&,String&);     String Substr(int index,int count);//从index开始提取count个字符的子串     int Find(char c,int start);//从下标start开始找到c后，返回字符c在本串的下标     int IsEmpty();//判本串是否为空串     void clear();//清本串为空串     void Print();             //字符串的输出函数     ~String()                     //析构函数     {if (ss) delete []ss;}};String::String(char *s)     //带参数的构造函数{     int len=strlen(s);     if (len>0)     {         ss=new char[len+1];         strcpy(ss,s);     }     else ss=0;     length=len;}String::String(String& s)//定义拷贝构造函数{     if (ss) delete[]ss;     if (s.length>0)     {         ss=new char[s.length+1];         strcpy(ss,s.ss);     }     else ss=0;     length=s.length;}String& String::operator =(String& s){//重载“=”运算符     if (ss) delete[] ss;     if (s.length>0)     {         ss=new char[s.length+1];         strcpy(ss,s.ss);     }     else ss=0;     length=s.length;     return *this;}void String::Print()                 //字符串的输出函数{     //cout<<"length="<<length<<",string=";     if (length>0)         cout<<ss<<endl;     else         cout<<"<null>"<<endl;}String& String::operator =(char *s){//重载“=”运算符     if (ss) delete[] ss;     int len=strlen(s);     if (len>0)     {         ss=new char[len+1];         strcpy(ss,s);     }     else ss=0;     length=len;     return *this;}String operator +(String &s1,String &s2){     char *t;     int l1,l2;     l1=s1.length;     l2=s2.length;     if (l1+l2>0)     {         t=new char[l1+l2+1];         if (l1>0)         {             strcpy(t,s1.ss);             if (l2>0)   strcat(t,s2.ss);         }         else   //l1=0时,l2>0             strcpy(t,s2.ss);     }     else t="\0";     return String(t);}String& String::operator +=(String& s){     String temp;     temp=*this+s;     *this=temp;     return *this;}String& String::operator +=(char *s){     String temp;     temp=*this+s;     *this=temp;     return *this;}String operator +(String &s1,char* s2){     char* t;     int l1,l2;     l1=s1.length;     l2=strlen(s2);     if (l1+l2>0)     {         t=new char[l1+l2+1];         if (l1>0)         {             strcpy(t,s1.ss);             if (l2>0) strcat(t,s2);         }   else strcpy(t,s2);     }     else t="\0";     return String(t);}String operator +(char* s1,String &s2){    char* t;    int l1,l2;    l1=strlen(s1);    l2=s2.length;    if (l1+l2>0)    {       t=new char[l1+l2+1];       if (l1>0)       {          strcpy(t,s1);          if (l2>0) strcat(t,s2.ss);       }       else strcpy(t,s2.ss);    }    else t="\0";    return String(t);}int operator ==(String &s1,String &s2){    if (strcmp(s1.ss,s2.ss)==0)       return true;    else       return false;}int operator ==(String &s1,char* s2){    if (strcmp(s1.ss,s2)==0)       return true;    else       return false;}int operator ==(char* s1,String &s2){    if (strcmp(s1,s2.ss)==0)       return true;    else       return false;}int operator >(String &s1,String &s2){    if (strcmp(s1.ss,s2.ss)>0)       return true;    else       return false;}int String::operator >(char* s2){     if (strcmp(this->ss,s2)>0)         return true;     else         return false;}int operator >(char* s1,String &s2){     if (strcmp(s1,s2.ss)>0)         return true;     else         return false;}char& String::operator [](int n){     if (n<0 || n>=length)     {         cout<<"下标超界!\n";         exit(0);     }     return this->ss[n];}ostream& operator <<(ostream &os,String& s){   //友元函数,不能用成员函数    if (s.ss)       os<<s.ss;    else       os<<"<null>"; return os;}istream& operator >>(istream &is,String &s){   //友元函数,不能用成员函数    if (s.ss) delete[] s.ss;    char *str=new char[2048];    is>>str    int len=strlen(str);    if (len>0)    {       s.ss=new char[len+1];       strcpy(s.ss,str);       s.length=len;    }    else { s.ss=0;s.length=0; }    delete[] str;    return is;}void strcat(String& s1,char *s2){//友元函数,重载strcat()函数,第一个参数为char*的不需重载    int l1,l2;    l1=s1.length;    l2=strlen(s2);    if (l1+l2>0)    {       if (l1>0)       {          char* t;          t=new char[l1+1];          strcpy(t,s1.ss);          delete []s1.ss;          s1.ss=new char[l1+l2+1];          strcpy(s1.ss,t);          if (l2>0) strcat(s1.ss,s2);       }       else     //l1=0,l2>0的情况          strcpy(s1.ss,s2);       s1.length=l1+l2;    }    //l1+l2=0时,s1仍为空串,故不需处理}void main( ){     String s1="Nanjing",s2="Shanghai",s3,a("aa"),b("bb");     char str[100]="Computer department,";     cout<<"String s1="<<s1<<endl;//输出字符串s1(重载<<运算符)     cout<<"String s2="<<s2<<endl;//输出字符串s2(重载<<运算符)     cout<<"String s3="<<s3<<endl;     cout<<"String   a="<<a<<endl;     cout<<"String   b="<<b<<endl;     s3=s1;                     //调用operator =(String&),重载“=”运算符     cout<<"执行s3=s1;后,s3="<<s3<<endl;     s3="Beijing";             //调用operator =(char*)     cout<<"执行s3=\"Beijing\";后,s3="<<s3<<endl; s3+=s2;                     //operator +=(String&),重载“+=”运算符     cout<<"执行s3+=s2;后,s3="<<s3<<endl;     s3=s1+s2;                 //String+String,重载“+”     cout<<"执行s3=s1+s2;后,s3="<<s3<<endl;     s3=s1+"Tianjin";         //String+char*,重载“+”     cout<<"执行s3=s1+\"Tianjin\"后,s3="<<s3<<endl;     s3="Guangzhou"+s2;         //char* +String,重载“+”     cout<<"执行s3=\"Guangzhou\"+s2;后,s3="<<s3<<endl;     s3=a+b;                     //空String+空String     cout<<"执行s3=a+b;后,s3="<<s3<<endl;     s3+="Public";     cout<<"接着执行s3+=\"Public\";后,s3="<<s3<<endl;     cout<<"测试String==String功能：";     if (s1==s3)             //operator ==(String,String),重载“==”         cout<<s1<<'='<<s3<<endl;     else         cout<<s1<<"!="<<s3<<endl;     cout<<"测试String==char*功能：";     if (s3=="Public")     //operator ==(String,char*),重载“==”         cout<<s3<<'='<<"Public"<<endl;     else         cout<<s3<<"!="<<"Public"<<endl;     cout<<"测试char*==String功能：";     if ("Public1"==s3)     //operator ==(char*,String),重载“==”         cout<<s3<<'='<<"Public1"<<endl;     else         cout<<s3<<"!="<<"Public1"<<endl;     char *sa="WuHan";     cout<<"测试String>char*功能：";     if (s2>sa)             //operator >(String,String),重载“>”         cout<<s2<<'>'<<sa<<endl;     else         cout<<s2<<"<="<<sa<<endl; cout<<"测试String>String功能：";     if (s2>s3)             //operator >(String,String),重载“>”         cout<<s2<<'>'<<s3<<endl;     else         cout<<s2<<"<="<<s3<<endl;     cout<<"测试char*>String功能：";     if (sa>s3)             //operator >(String,String),重载“>”         cout<<sa<<'>'<<s3<<endl;     else         cout<<sa<<"<="<<s3<<endl;     cout<<"strlen(s1)="<<strlen(s1)<<endl;       //有了类型转换函数，字符串处     cout<<"strcmp(s1,s2)="<<strcmp(s1,s2)<<endl;//理函数不用重载就可直接使用     strcat(s1," University");                     //调用重载函数strcat(String,char*)     cout<<"执行strcat(s1,\" University\");后，s1="<<s1<<endl;     strcat(s2,s3);     //调用重载函数strcat(String,char*):自动将s3转换成char*类型     cout<<"执行strcat(s2,s3);后，s2="<<s2<<endl;     s2.Print();     cout<<"str="<<str<<endl;     strcat(str,s1);     //调用库函数strcat(char*,char*):自动将s1转换成char*类型     cout<<"执行strcat(str,s1);后，str="<<str<<endl;     cout<<"测试提取运算符“>>”，请输入一串字符：";cin>>s3;     //重载“>>”运算符     cout<<"输入的字符串是："<<s3<<endl;     cout<<"输入的字符串长度是："<<strlen(s3)<<endl;     cout<<"测试下标运算符：\n";     cout<<"s3中下标为2的字符为："<<s3[2]<<endl;     s3[2]='A';     cout<<"执行s3[2]='A'后，s3变为："<<s3<<endl;}