自编字符串类

1、/ 我希望利用这个String类和其他少数类外定义的函数可以实现对 String类的对象和C字符串 实现 "无缝操作" , 即对两者能使用相同的表达式进行类似或相同的操作而无需加以区分/ 类外面定义类中的函数（成员或友元）定义顺序与他们在类中出现的顺序一致，且用注释编号以便查看/ char * 为0的情况有点烦人，因为字符串处理函数不能处理它，而且不能使用cout输出，使得编程时需要增加很多额外的代码/ 删掉了转换函数const char *，因为它使得减法和某些逻辑运算出错(overloads have two similar covernsions)/ 类String中

2、的初始化函数String( const char * )相当重要#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 ; /输出字符串friend ostream & operator << ( ostream & , const String & ); /No.1.1 String() if(Sp) delete Sp; friend bool IsIn( const String &, const char ); /No.2 母字符串为第一个参数，要查找的字符为第二个参数/能处理(String，char), (char *，

4、char)friend bool IsSubStr( const String &, const String & ); /No.3 母字符串为第一个参数，要查找的子字符串为第二个参数/能处理(String，String)，(String，char*)，(char *，String)和(char *,char *)/默认空字符串为任意字符串的子字符串int GetLen() return Length; /取长度char * GetString() return Sp; /取字符串/当指针值为0时，返回后，在调用函数中的操作可能会出事String & operator

5、= ( String & ); /No.4 /能处理 String=String 和String= char */因为 operator = 只能是成员函数，所以不能处理第一个操作数是char*类型的情况/下面从No.5到No.7.6重载的操作符的操作数必须至少有一个是String类的对象，/如果两个操作数都是char*类型的，则必须在至少其中一个之前加上强制转换符String,/这可以说是一个比较大的缺陷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/能处理 String+=String 和 String+=char*，

8、下同/对于char*+=String 和 char*+=char*，必须在char*前加上强制转换符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