数据结构与程序设计(17)String-Operator-overload

1/21/2026数据结构与程序设计1课程内容安排CString与String的比较。讨论C++中StringClass的实现方法。1/21/2026数据结构与程序设计2CString与StringClassstringclass:stringclassinthestandardlibraryaccessedby#include<string>Cstrings:canbeaccessedby#include<cstring>

AStringconstantisstoredasachararray.即一个常量的string被认为是cstringe.g.:“Helloeveryone”//cstringstrings=“Helloeveryone”//Stringobject

1/21/2026数据结构与程序设计3WhatisaCString?ChararrayACstringisachararrayterminatedbythenullcharacter‘\0’(withASCIIvalue0).ACstringvariablecanbeinitializedinitsdeclarationinfollowingways.

charmessage[8]={‘H’,‘e’,‘l’,‘l’,‘o’,‘\0’};

charmessage[8]=“Hello”;Char*message=“hello”;message[0][1][2][3][4][5][6][7]‘H’‘e’‘l’‘l’‘o’‘\0’1/21/2026数据结构与程序设计4字符串(String)字符串是n(0)个字符的有限序列，记作S:“c1c2c3…cn”其中，S是串名字

“c1c2c3…cn”

是串值

ci是串中字符

n是串的长度。

1/21/2026数据结构与程序设计5functionsthatmanipulateC-strings//字符串的拷贝操作。char*strcpy(char*to,char*from);Pre:Thestringfromhasbeeninitialized.Post:Thefunctioncopiesstringfromtostringto,including‘\0’;itreturnsapointertothebeginningofthestringto.//将from指向的内容链接在to的内容之后char*strcat(char*to,char*from);Pre:Thestringsfromandtohavebeeninitialized.Post:Thefunctioncopiesstringfromtotheendofstringto,including‘\0’;itreturnsapointertothebeginningofthestringto.1/21/2026数据结构与程序设计6functionsthatmanipulateC-strings//求字符串的长度intstrlen(char*s);Pre:Thestringshasbeeninitialized.Post:Thefunctionreturnsthelengthofthestrings,notincludingthenullbyte‘\0’attheendofthestrings.//字符串的比较操作。intstrcmp(char*s1,char*s2);Pre:Thestringss1ands2havebeeninitialized.Post:Thefunctioncomparesstrings1tostrings2;itreturns<0ifs1<s2,0ifs1==s2,or>0ifs1>s2.1/21/2026数据结构与程序设计7functionsthatmanipulateC-strings//返回s2第一次在s1中出现的位置。char*strstr(char*s1,char*s2);Pre:Thestringss1ands2havebeeninitialized.Post:Thefunctionreturnsapointertothefirstoccurrenceofthestrings2inthestrings1,oritreturnsNULLifthestrings2isnotpresentins1.1/21/2026数据结构与程序设计8StringsinC char*p="helloworld";//can'tbewritten char*q=newchar[strlen(p)+1]; strcpy(q,p); cout<<q<<endl; //q=p; p=q; *p='H';cout<<q<<endl; cout<<p<<endl;1/21/2026数据结构与程序设计9StringsinCchar*strcpy(char*to,char*from){ inti; for(i=0;from[i]!='\0';i++)to[i]=from[i]; to[i]='\0'; returnto;}1/21/2026数据结构与程序设计10StringsinCintstrlen(char*s){inti;for(i=0;s[i]!='\0';i++);return(i);}1/21/2026数据结构与程序设计11ComparisonBOOKP234Figure6.5“Importantstring”“acquiresanalias”S2=s1S2S11/21/2026数据结构与程序设计12ComparisonC-stringsarewidelyavailable.C-stringsareveryefficient.C-stringobjectsarenotencapsulated.C-stringsareeasytomisuse,withconsequencesthatcanbedisastrous.ItiseasyforaclienttocreateeithergarbageoraliasesforC-stringdata.1/21/2026数据结构与程序设计13//******************************************************//PrintNameprogram//Thisprogramprintsanameintwodifferentformats//******************************************************#include<iostream> //forcoutandendl#include<string> //fordatatypestringusingnamespacestd;conststringFIRST=“Herman”;//Person’sfirstnameconststringLAST=“Smith”;//Person’slastnameconstcharMIDDLE=‘G’;//Person’smiddleinitialC++Program--STLSTRING1/21/2026数据结构与程序设计14C++CodeContinuedintmain(){stringfirstLast;//Nameinfirst-lastformatstringlastFirst; //Nameinlast-firstformat

firstLast=FIRST+““+LAST;cout<<“Nameinfirst-lastformatis“<<endl <<firstLast<<endl;lastFirst=LAST+“,“+FIRST+’’;cout<<“Nameinfirst-lastformatis“<<endl <<lastFirst<<MIDDLE<<’.’<<endl;return0;}1/21/2026数据结构与程序设计15OutputofProgram

Nameinfirst-lastformatisHermanSmithNameinlast-first-initialformatisSmith,HermanG.1/21/2026数据结构与程序设计16ImplementationofStringClassclassString{public://methodsofthestringADT String(); ~String(); String(constString©);//copyconstructor String(constchar*copy);//conversionfromC-string String(List<char>©);//conversionfromList voidoperator=(constString©); constchar*c_str()const;//conversiontoC-stylestringprotected: char*entries; intlength;};1/21/2026数据结构与程序设计17运算符重载，全局方法booloperator==(constString&rst,constString&second);booloperator>(constString&rst,constString&second);booloperator<(constString&rst,constString&second);booloperator>=(constString&rst,constString&second);booloperator<=(constString&rst,constString&second);booloperator!=(constString&rst,constString&second);1/21/2026数据结构与程序设计18StringconstructorString::String(){ entries=newchar[1]; entries[0]='\0'; length=0;}1/21/2026数据结构与程序设计19StringconstructorString::String(List<char>&in_list)/*Post:TheStringisinitializedbythecharacterListin_list.*/{ length=in_list.size(); entries=newchar[length+1]; for(inti=0;i<length;i++)in_list.retrieve(i,entries[i]); entries[length]='\0';}1/21/2026数据结构与程序设计20ImplementationofStringClassconstchar*String::c_str()const/*Post:ApointertoalegalC-stringobjectmatchingtheStringisreturned.*/{ return(constchar*)entries;}1/21/2026数据结构与程序设计21全局函数的实现

OperatorOverloadbooloperator==(constString&first,constString&second)/*Post:ReturntrueiftheStringfirstagreeswithStringsecond.Else:Returnfalse.*/{ returnstrcmp(first.c_str(),second.c_str())==0;}1/21/2026数据结构与程序设计22FunctionOverloadvoidstrcat(String&add_to,constString&add_on)/*Post:ThefunctionconcatenatesStringadd_onontotheendofStringadd_to.*/{constchar*cfirst=add_to.c_str();constchar*csecond=add_on.c_str();char*copy=newchar[strlen(cfirst)+strlen(csecond)+1];strcpy(copy,cfirst);strcat(copy,csecond);add_to=copy;//?delete[]copy;}1/21/2026数据结构与程序设计23MainProgramStringread_in(istream&input)/*Post:ReturnaStringread(ascharactersterminatedbyanewlineoranend-of-filecharacter)fromanistreamparameter.*/{List<char>temp;intsize=0;charc;while((c=input.peek())!=EOF&&(c=input.get())!='\n')temp.insert(size++,c);Stringanswer(temp);returnanswer;}1/21/2026数据结构与程序设计24MainProgramvoidwrite(String&s)/*Post:TheStringparametersiswrittentocout.*/{cout<<s.c_str()<<endl;}注意：Char*p=“hello”;Cout<<p;//将输出字符串hello的值。1/21/2026数据结构与程序设计25MainProgramostream&operator<<(ostream&output,Strings1){ ou