How to express string semantic (2)?

(2)string  and related  classes in  c++ STL 
string class  is a portable class.it can be used in many platforms,such as windows,linux,unix,etc!
it encapsulates string semantic and provides many useful member fuctions !
when we use it, don't worry memory overflow,beause it can allocate memory space itself.
In STL,it is defined in header <string>  and std namespace.so if you use it, you will add
#include <string> and
using std::string;or
using std::namespace or
in programe use
std::string define string.
for example:

#include  < string >
#include  < iostream >
int  main()
{
  std::string str;
  std::cin>>str;
  std::cout<<"your input:"<<str<<std::endl; 
}

member funtions in string is very useful.
I  won't discuss it in detail,for many good books do it!
Although string class isn't a container class,it provides similar interfaces,such as begin(),end().
so you can use it like a container class so it can agree with many generic algorithm  in header <algorithm> .
for example:

string str1(  " Alpha Beta Gamma Delta "  );
   string::size_type loc  =  str1.find(  " Omega " ,  0  );
    if ( loc  !=  string::npos )  {
     cout << "Found Omega at " << loc << endl;
   }   else   {
     cout << "Didn't find Omega" << endl;         
   }
or
string str1(  " Alpha Beta Gamma Delta "  );
   string::const_iterator loc  =  find( str1.begin(),str1.end(), " Omega " );
    if ( loc  !=  str1.end() )  {
     cout << "Found Omega at " << loc << endl;
   }   else   {
     cout << "Didn't find Omega" << endl;         
   }

and so on!
some useful associated classes are introduced here.
they are defined in header <sstream>:

• stringstream - allows input and output
• istringstream - allows input only
• ostringstream - allows output only

  An ostringstream object can be used to write to a string. This is similar to the C sprintf() function. For example:
   

   ostringstream s1;
     int  i  =   22 ;
    s1  <<   " Hello  "   <<  i  <<  endl;
    string s2  =  s1.str();
    cout  <<  s2;
  

  
  An istringstream object can be used to read from a string. This is similar to the C sscanf() function. For example:
   

   istringstream stream1;
  string string1  =   " 25 " ;
    stream1.str(string1);
     int  i;
    stream1  >>  i;
    cout  <<  i  <<  endl;   //  displays 25
  

  
    You can also specify the input string in the istringstream constructor as in this example:

   string string1  =   " 25 " ;
    istringstream stream1(string1);
     int  i;
    stream1  >>  i;
    cout  <<  i  <<  endl;   //  displays 25
  

   A stringstream object can be used for both input and output to a string like an fstream object.

   when you are familar with these classes,you are able to handle with string-related problem!