设计一个字符串类 MyString，具有构造函数、析构函数、

解：

#include <iostream.h>
#include <string.h>
class MyString
{
public:
MyString();
MyString(const char *const);
MyString(const MyString &);
~MyString();
char & operator[](unsigned short offset);
char operator[](unsigned short offset) const;
MyString operator+(const MyString&);
void operator+=(const MyString&);
MyString & operator= (const MyString &);
unsigned short GetLen()const { return itsLen; }
const char * GetMyString() const { return itsMyString; }
private:
MyString (unsigned short); // private constructor
char * itsMyString;
unsigned short itsLen;
};
MyString::MyString()
{
itsMyString = new char[1];
itsMyString[0] = '\0';
itsLen=0;
}
MyString::MyString(unsigned short len)
{
itsMyString = new char[len+1];
for (unsigned short i = 0; i<=len; i++)
itsMyString[i] = '\0';
itsLen=len;
}
MyString::MyString(const char * const cMyString)
{
itsLen = strlen(cMyString);
itsMyString = new char[itsLen+1];
for (unsigned short i = 0; i<itsLen; i++)
itsMyString[i] = cMyString[i];
itsMyString[itsLen]='\0';
}
MyString::MyString (const MyString & rhs)
{
itsLen=rhs.GetLen();
itsMyString = new char[itsLen+1];
for (unsigned short i = 0; i<itsLen;i++)
itsMyString[i] = rhs[i];
itsMyString[itsLen] = '\0';
}
MyString::~MyString ()
{
delete [] itsMyString;
itsLen = 0;
}
MyString& MyString::operator=(const MyString & rhs)
{
if (this == &rhs)
return *this;
delete [] itsMyString;
itsLen=rhs.GetLen();
itsMyString = new char[itsLen+1];
for (unsigned short i = 0; i<itsLen;i++)
itsMyString[i] = rhs[i];
itsMyString[itsLen] = '\0';
return *this;
}
char & MyString::operator[](unsigned short offset)
{
if (offset > itsLen)
return itsMyString[itsLen-1];
else
return itsMyString[offset];
}
char MyString::operator[](unsigned short offset) const
{
if (offset > itsLen)
return itsMyString[itsLen-1];
else
return itsMyString[offset];
}
MyString MyString::operator+(const MyString& rhs)
{
unsigned short totalLen = itsLen + rhs.GetLen();
MyString temp(totalLen);
for (unsigned short i = 0; i<itsLen; i++)
temp[i] = itsMyString[i];
for (unsigned short j = 0; j<rhs.GetLen(); j++, i++)
temp[i] = rhs[j];
temp[totalLen]='\0';
return temp;
}
void MyString::operator+=(const MyString& rhs)
{
unsigned short rhsLen = rhs.GetLen();
unsigned short totalLen = itsLen + rhsLen;
MyString temp(totalLen);
for (unsigned short i = 0; i<itsLen; i++)
temp[i] = itsMyString[i];
for (unsigned short j = 0; j<rhs.GetLen(); j++, i++)
temp[i] = rhs[i-itsLen];
temp[totalLen]='\0';
*this = temp;
}
int main()
{
MyString s1("initial test");
cout << "S1:\t" << s1.GetMyString() << endl;
char * temp = "Hello World"; 
s1 = temp;
cout << "S1:\t" << s1.GetMyString() << endl;
char tempTwo[20];
strcpy(tempTwo,"; nice to be here!"); 
s1 += tempTwo;
cout << "tempTwo:\t" << tempTwo << endl;
cout << "S1:\t" << s1.GetMyString() << endl;
cout << "S1[4]:\t" << s1[4] << endl; 
s1[4]='x';
cout << "S1:\t" << s1.GetMyString() << endl;
cout << "S1[999]:\t" << s1[999] << endl;
MyString s2(" Another myString"); 
MyString s3;
s3 = s1+s2;
cout << "S3:\t" << s3.GetMyString() << endl;
MyString s4;
s4 = "Why does this work?";
cout << "S4:\t" << s4.GetMyString() << endl; 
return 0;
}