自編字符串類

1、/ 我希望利用這個String類和其他少數類外定義的函數可以實現對 String類的對象和C字符串 實現 "無縫操作" , 即對兩者能使用相同的表達式進行類似或相同的操作而無需加以區(qū)分/ 類外面定義類中的函數（成員或友元）定義順序與他們在類中出現的順序一致，且用注釋編號以便查看/ char * 為0的情況有點煩人，因為字符串處理函數不能處理它，而且不能使用cout輸出，使得編程時需要增加很多額外的代碼/ 刪掉了轉換函數const char *，因為它使得減法和某些邏輯運算出錯(overloads have two similar covernsions)/ 類String中

2、的初始化函數String( const char * )相當重要#include <iostream>#include <cstring>using namespace std;class String protected:int Length;char *Sp;public:String() Sp=0; Length=0; String( const String & ); /No.1.0String( const char * s )if (!s) Length=0; Sp=0; return ; Length = strlen( s ) ;Sp = new

3、 char Length + 1 ;strcpy ( Sp, s );void show() if(Sp) cout<< Sp ; /輸出字符串friend ostream & operator << ( ostream & , const String & ); /No.1.1 String() if(Sp) delete Sp; friend bool IsIn( const String &, const char ); /No.2 母字符串為第一個參數，要查找的字符為第二個參數/能處理(String，char), (char *，

4、char)friend bool IsSubStr( const String &, const String & ); /No.3 母字符串為第一個參數，要查找的子字符串為第二個參數/能處理(String，String)，(String，char*)，(char *，String)和(char *,char *)/默認空字符串為任意字符串的子字符串int GetLen() return Length; /取長度char * GetString() return Sp; /取字符串/當指針值為0時，返回后，在調用函數中的操作可能會出事String & operator

5、= ( String & ); /No.4 /能處理 String=String 和String= char */因為 operator = 只能是成員函數，所以不能處理第一個操作數是char*類型的情況/下面從No.5到No.7.6重載的操作符的操作數必須至少有一個是String類的對象，/如果兩個操作數都是char*類型的，則必須在至少其中一個之前加上強制轉換符String,/這可以說是一個比較大的缺陷friend String operator + ( const String &, const String & ); /No.5friend String ope

6、rator - ( const String &, const String & ); /No.6friend bool operator < ( const String &, const String & ); /No.7.1friend bool operator > ( const String &, const String & ); /No.7.2friend bool operator <= ( const String &, const String & ); /No.7.3friend bool

7、 operator >= ( const String &, const String & ); /No.7.4friend bool operator = ( const String &, const String & ); /No.7.5friend bool operator != ( const String &, const String & ); /No.7.6String operator += ( const String &) ; /No.8/能處理 String+=String 和 String+=char*，

8、下同/對于char*+=String 和 char*+=char*，必須在char*前加上強制轉換符String，下同String operator -= ( const String & ); /No.9; / Start defining functions in class String/No.1.0String:String( const String &s )Length = s.Length;if ( s.Sp ) Sp = new char Length + 1 ;strcpy( Sp, s.Sp );else Sp=0;/No.1.1ostream &

9、operator << ( ostream &stream, const String &str )if(str.Sp) stream << str.Sp ;return stream;/No.2bool IsIn ( const String &str, const char c )if ( !str.Sp ) return 0;const char *p = str.Sp ; while( *p ) if( *p + = c ) return 1;return 0;/No.3bool IsSubStr ( const String &

10、str1, const String &str2 )if ( !str2.Sp ) return 1;else if ( !str1.Sp ) return 0;else if ( strstr( str1.Sp, str2.Sp ) ) return 1;else return 0;/No.4String & String:operator = ( String &str )if (Sp) delete Sp;Length = str.Length;if( str.Sp ) Sp = new char Length + 1 ;strcpy( Sp, str.Sp );

11、else Sp=0;return *this;/No.5String operator + ( const String &s1, const String &s2 )String temp;temp.Length = s1.Length + s2.Length;if( !temp.Length ) return temp; temp.Sp = new char temp.Length + 1 ;if( s1.Sp ) strcpy( temp.Sp, s1.Sp );if( s2.Sp ) strcat( temp.Sp, s2.Sp );return temp;/No.6S

12、tring operator - ( const String &str1, const String &str2 ) if( (! str1.Length) | (! str2.Length) ) return str1;int i=0;char *p1=str1.Sp, *p2=0;String temp;if( p2=strstr( str1.Sp, str2.Sp ) ) temp.Length = str1.Length - str2.Length;temp.Sp = new char temp.Length + 1 ;while( p1<p2 ) temp.S

13、pi+=*p1+ ;p1 += str2.Length;while( temp.Spi+=*p1+ ) ;elsetemp.Length = str1.Length;temp.Sp = new char str1.Length + 1 ;strcpy( temp.Sp, str1.Sp );return temp;/No.7.1bool operator < ( const String &str1, const String &str2 )if( str1.Sp && str2.Sp ) return ( strcmp( str1.Sp, str2.Sp

14、 ) < 0 );else if ( str2.Sp ) return true;else return false;/No.7.2bool operator > ( const String &str1, const String &str2 )if ( str1.Sp && str2.Sp ) return ( strcmp( str1.Sp, str2.Sp ) > 0 );else if ( str1.Sp ) return true;else return false;/No.7.3bool operator <= ( cons

15、t String &str1, const String &str2 )return !( str1 > str2 );/No.7.4bool operator >= ( const String &str1, const String &str2 )return !( str1 < str2 );/No.7.5bool operator = ( const String &str1, const String &str2 )if( str1.Sp && str2.Sp ) return !( strcmp( s

16、tr1.Sp, str2.Sp ) );else if ( (!str1.Sp) && (!str2.Sp) ) return true;else return false;/No.7.6bool operator != ( const String &str1, const String &str2 )return !( str1=str2 );/No.8String String:operator += ( const String &str )(*this) = (*this) + str;return *this;/No.9String Stri

17、ng:operator -= ( const String &str )(*this) = (*this) - str;return *this;int main()String str1("I love you"), str2(str1);str1.show();cout << 'n' << str2 << 'n'cout <<"n-n"cout.setf( ios:boolalpha );char ch='o'String str3("y

18、ou");cout<< IsIn( str1, ch ) <<endl;cout<< IsIn( "I love you", ch ) <<endl;cout<< IsSubStr( str1, str3 ) << endl;cout<< IsSubStr( str1, "you" ) << endl;cout<< IsSubStr( "I love you", str3 ) << endl;cout<

19、;< IsSubStr( "I love you", "you" ) << endl;cout<< "n-n"cout<< "The length of str1 is " << str1.GetLen() <<endl;char *s1 = str1.GetString();cout<< "The string of str1 is : " << s1 << endl;cout<<

20、 "n-n"String str4("I love you"), str5(", Jesus Christ"), str6, str7("Christ"), str8;str6 = str4 + str5;cout<< str6 <<endl;cout<< str4 + ", Jesus Christ" <<endl;cout<< "I love you" + str5 <<endl;cout<&l

21、t; "I love you" + (String)", Jesus Christ" <<endl;cout<< str6 - str7 <<endl;cout<< str6 - "Christ" <<endl;cout<< "I love you, Jesus Christ" - str7 <<endl;cout<< "I love you, Jesus Christ" - (String)"Christ" <<endl;str8 = str4 + str5 - str7 - " you," - "I "cout<< str8 <<endl;cout<<"n-n"String str9("Good"), str