This slides helps to understand how the C++ built-in string is built.

1. C++ Algorithms
Prepared by
Mohammed Sikander
Team Lead
CranesVarsity

2. Mohammed Sikander www.cranessoftware.com
int main( )
{
char *ptr = "SIKANDER";
string str = "SIKANDER";
cout << sizeof(ptr) << endl;
cout << sizeof(str) << endl;
}

3. Mohammed Sikander www.cranessoftware.com
int main( )
{
char *ptr = "SIKANDER";
string str = "SIKANDER";
ptr[0] = ‘A’;
str[0] = 'A';
cout << ptr << endl;
cout << str << endl;
}

4. Mohammed Sikander www.cranessoftware.com
int main( )
{
char *ptr ;
string str ;
cin >> ptr;
cin >> str;
cout << ptr << endl;
cout << str << endl;
}

5. Mohammed Sikander www.cranessoftware.com
class MyString
{
char *ptr;
};
int main( )
{
MyString ms1;
cout << sizeof(ms1) << endl;
}
class MyString
{
char *ptr;
};
int main( )
{
MyString ms1;
cout << sizeof(ms1) << endl;
MyString ms2 ("ASDF");
}

6. Mohammed Sikander www.cranessoftware.com
class MyString
{
char *str;
public : MyString(const char *ptr)
{
int len = strlen(ptr);
str = new char[len + 1];
strcpy(str , ptr);
}
};
int main( )
{
MyString ms1;
cout << sizeof(ms1) << endl;
MyString ms2 ("ASDF");
}
class MyString
{
char *str;
public : MyString( )
{
str = NULL;
}
MyString(const char *ptr)
{
int len = strlen(ptr);
str = new char[len + 1];
strcpy(str , ptr);
}
};

7. Mohammed Sikander www.cranessoftware.com
class MyString
{
char *str;
public : MyString( )
{ str = NULL; }
MyString(char *ptr)
{
int len = strlen(ptr);
str = new char[len + 1];
strcpy(str , ptr);
}
char operator [ ](int index)
{
return str[index];
}
};
int main( )
{
MyString ms2 ("ASDF");
for(int i = 0 ; i < 4 ; i++)
{
ms2[i] = ms2[i] + 1;
cout << ms2[i] << endl;
}
}
int main( )
{
MyString ms2 ("ASDF");
for(int i = 0 ; i < 4 ; i++)
cout << ms2[i] << endl;
}

8. Mohammed Sikander www.cranessoftware.com
class MyString
{
char *str;
public : MyString( )
{ str = NULL; }
MyString(const char *ptr)
{
int len = strlen(ptr);
str = new char[len + 1];
strcpy(str , ptr);
}
char & operator [ ](int index)
{
return str[index];
}
};
int main( )
{
MyString ms2 ("ASDF");
for(int i = 0 ; i < 4 ; i++)
{
ms2[i] = ms2[i] + 1;
cout << ms2[i] << endl;
}
}
int main( )
{
MyString ms2 ("ASDF");
for(int i = 0 ; i < 4 ; i++)
cout << ms2[i] << endl;
}

9. Mohammed Sikander www.cranessoftware.com
MyString MyString ::operator +(const MyString &rhs) const
{
MyString temp;
int len = strlen(str) + strlen(rhs.str);
temp.str = new char[len + 1];
strcpy(temp.str , str);
strcat(temp.str , rhs.str);
return temp;
}
int main( )
{
MyString firstname = “MOHAMMED”;
MyString lastname = “SIKANDER”;
MyString fullname = firstname +lastname;
firstname.display() ;
lastname.display() ;
fullname.display();
}
class MyString
{
char *str;
public : //relevent constructors are provided
void display( )
{ cout << str << endl; }
MyString operator +(const MyString &rhs) const
};

10. Mohammed Sikander www.cranessoftware.com
class MyString
{
char *str;
public : //Assume require constructors are present
bool operator >(const MyString &rhs)
{ return strcmp(str , rhs.str) > 0 ? true : false; }
bool operator >=(const MyString &rhs)
{ return strcmp(str , rhs.str) >= 0 ? true : false;}
bool operator <(const MyString &rhs)
{ return strcmp(str , rhs.str) < 0 ? true : false; }
bool operator <=(const MyString &rhs)
{ return strcmp(str , rhs.str) <= 0 ? true : false; }
bool operator ==(const MyString &rhs)
{ return strcmp(str , rhs.str) == 0 ? true : false; }
bool operator !=(const MyString &rhs)
{ return strcmp(str , rhs.str) != 0 ? true : false; }
};
int main( )
{
MyString s1 = “BANGALORE”;
MyString s2= “DELHI”;
MyString s3 = “BANGALORE”;
cout << (s1 > s2 ? S1 : s2);
if(s1 == s3)
cout << “EQUAL”;
else
cout<<“NOT EQUAL”
}

11. Mohammed Sikander www.cranessoftware.com
class MyString
{
char *str;
public : MyString( )
{ str = NULL; }
MyString(const char *ptr)
{
int len = strlen(ptr);
str = new char[len + 1];
strcpy(str , ptr);
}
};
int main( )
{
MyString s1 = "SIKANDER";
return 0;
}
Run valgrind and detect memory leakage.
$valgrind ./a.out

12. Mohammed Sikander www.cranessoftware.com
class MyString
{ char *str;
public : MyString( )
{ str = NULL; }
MyString(const char *ptr)
{
int len = strlen(ptr);
str = new char[len + 1];
strcpy(str , ptr);
}
~MyString( )
{
delete [ ] str;
}
};
int main( )
{
MyString s1 = "SIKANDER";
return 0;
}
Run valgrind and detect memory leakage.
$valgrind ./a.out

13. Mohammed Sikander www.cranessoftware.com
class MyString
{
char *str;
public :
MyString(char *ptr)
{
cout <<“Constructor n”;
int len = strlen(ptr);
str = new char[len + 1];
strcpy(str , ptr);
}
~MyString( )
{
cout <<“Destructor ” << str;
delete [ ] str;
}
};
int main( )
{
MyString s1 = “SIKANDER”;
MyString s2 = s1;
}

14. Mohammed Sikander www.cranessoftware.com
class MyString
{
char *str;
public :
MyString(const char *ptr)
{
cout <<“Constructor n”;
int len = strlen(ptr);
str = new char[len + 1];
strcpy(str , ptr);
}
MyString(const MyString &old){
cout <<“Copy Constructor”;
str = new char[strlen(old.str) + 1];
strcpy(str , old.str);
}
~MyString( )
{
cout <<“Destructor n”;
delete [ ] str;
}
};
int main( )
{
MyString s1 = “SIKANDER”;
MyString s2 = s1;
}

15. Mohammed Sikander www.cranessoftware.com
class MyString
{ char *str;
public :
MyString( )
{ cout <<“Default Constructor n”;
str = NULL;
}
MyString(const char *ptr) {
cout <<“Constructor n”;
int len = strlen(ptr);
str = new char[len + 1];
strcpy(str , ptr);
}
~MyString( ) {
cout <<“Destructor n”;
delete [ ] str;
}
int main( )
{
MyString s1 = “SIKANDER”;
MyString s2;
s2 = s1;
}
MyString(const MyString &old){
cout <<“Copy Constructor”;
str = new char[strlen(old.str) + 1;
strcpy(str , old.str);
}
};

16. Mohammed Sikander www.cranessoftware.com
class MyString
{ char *str;
public :
MyString( )
{ cout <<“Default Constructor n”;
str = NULL;
}
MyString(const char *ptr) {
cout <<“Constructor n”;
int len = strlen(ptr);
str = new char[len + 1];
strcpy(str , ptr);
}
~MyString( ) {
cout <<“Destructor n”;
delete [ ] str;
}
MyString(const MyString &old){
cout <<“Copy Constructor”;
str = new char[strlen(old.str) + 1;
strcpy(str , old.str);
}
int main( )
{
MyString s1 = “SIKANDER”;
MyString s2;
s2 = s1;
}
MyString &operator = (const MyString &rhs)
{ cout <<“Assignment n”;
int len = strlen(rhs.str);
str = new char[len + 1];
strcpy(str , rhs.str);
return *this;
}
};

17. Mohammed Sikander www.cranessoftware.com
class MyString
{ char *str;
public :
MyString( )
{ cout <<“Default Constructor n”;
str = NULL;
}
MyString(const char *ptr) {
cout <<“Constructor n”;
int len = strlen(ptr);
str = new char[len + 1];
strcpy(str , ptr);
}
~MyString( ) {
cout <<“Destructor n”;
delete [ ] str;
}
MyString(const MyString &old){
cout <<“Copy Constructor”;
str = new char[strlen(old.str) + 1;
strcpy(str , old.str);
}
int main( )
{
MyString s1 = “SIKANDER”;
MyString s2 = “CHETHAN”;
s2 = s1;
}
MyString &operator = (const MyString &rhs)
{ cout <<“Assignment n”;
int len = strlen(rhs.str);
str = new char[len + 1];
strcpy(str , rhs.str);
return *this;
}
};

18. Mohammed Sikander www.cranessoftware.com
class MyString
{ char *str;
public :
MyString( )
{ cout <<“Default Constructor n”;
str = NULL;
}
MyString(const char *ptr) {
cout <<“Constructor n”;
int len = strlen(ptr);
str = new char[len + 1];
strcpy(str , ptr);
}
~MyString( ) {
cout <<“Destructor n”;
delete [ ] str;
}
MyString(const MyString &old){
cout <<“Copy Constructor”;
str = new char[strlen(old.str) + 1;
strcpy(str , old.str);
}
int main( )
{
MyString s1 = “SIKANDER”;
MyString s2 = “CHETHAN”;
s2 = s1;
}
MyString & operator = (const MyString &rhs)
{
this->~MyString();
int len = strlen(rhs.str);
str = new char[len + 1];
strcpy(str , rhs.str);
return *this;
}
};

19. Mohammed Sikander www.cranessoftware.com
class MyString
{ char *str;
public :
MyString( )
{ cout <<“Default Constructor n”;
str = NULL;
}
MyString(const char *ptr) {
cout <<“Constructor n”;
int len = strlen(ptr);
str = new char[len + 1];
strcpy(str , ptr);
}
~MyString( ) {
cout <<“Destructor n”;
delete [ ] str;
}
MyString(const MyString &old){
cout <<“Copy Constructor”;
str = new char[strlen(old.str) + 1;
strcpy(str , old.str);
}
int main( )
{
MyString s1 = “SIKANDER”;
MyString s2 = “CHETHAN”;
s2 = s2;
}
MyString & operator = (const MyString &rhs)
{
this->~MyString();
int len = strlen(rhs.str);
str = new char[len + 1];
strcpy(str , rhs.str);
return *this;
}
};

20. Mohammed Sikander www.cranessoftware.com
class MyString
{ char *str;
public :
MyString( )
{ cout <<“Default Constructor n”;
str = NULL;
}
MyString(const char *ptr) {
cout <<“Constructor n”;
int len = strlen(ptr);
str = new char[len + 1];
strcpy(str , ptr);
}
~MyString( ) {
cout <<“Destructor n”;
delete [ ] str;
}
MyString(const MyString &old){
cout <<“Copy Constructor”;
str = new char[strlen(old.str) + 1;
strcpy(str , old.str);
}
int main( )
{
MyString s1 = “SIKANDER”;
MyString s2 = “CHETHAN”;
s2 = s2;
}
MyString & operator = (const MyString &rhs)
{
if(this != &rhs)
{
this->~MyString();
int len = strlen(rhs.str);
str = new char[len + 1];
strcpy(str , rhs.str);
}
return *this;
}
};

21. Mohammed Sikander www.cranessoftware.com
class MyString
{ char *str;
public :
MyString( );
MyString(const char *ptr);
~MyString( );
MyString(const MyString &old);
friend ostream &operator << (ostream & , const MyString &);
friend istream &operator >> (istream & , MyString &);
};
int main( )
{
MyString s1;
MyString s2;
cout <<“Enter the string : “;
cin >> s1;
cout << s1<< endl;
}
ostream &operator << (ostream &out, const MyString &s)
{
out << s.str ;
return out;
}
istream &operator >> (istream &in, MyString &s)
{
char buffer[1024];
in >> buffer;
str = new char[strlen(buffer) + 1];
strcpy(str , buffer);
}

22. Mohammed Sikander www.cranessoftware.com
 For feedback and suggestions.
 Mail me at
mohammed.sikander@cranessoftware.com;