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cis155_Ch11b_sstream

1. Week 9. Ch.11, String Stream
2. String streams
3. String streams, cont.
4. String stream example
5. Unformatted I/O using String Stream
6. Stream Functionality
7. Credits

1. Week 9. Ch.11, String Stream

• Today:

  • Using memory buffer as stream of bytes

  • Key areas:

    • data -> text conversion

    • text -> data conversion

   

2. String streams

• A stringstream reads/writes from/to a string rather than a file or a keyboard/screen. For example,

  
  #include <cstdlib>
  #include <iostream>
  #include <sstream>
  
  using namespace std;
  
  // if possible, convert characters in s to floating-point value
  double str_to_double(string s)
  {
      istringstream is(s);
      //
      // make a stream so that we can read from s
      double d;
      is >> d;
      if ( !is ) throw runtime_error( "double format error" );
      return d;
  }//str_to_double
  
  
  // testing
  void doit()
  {
      double d1 = str_to_double( "12.4" );
      double d2 = str_to_double( "1.34e-3" );
      double d3 = str_to_double( "twelve point three" ); // error
  }//doit
  
  
  int main()
  {
      try {
          doit();
      }
      catch ( runtime_error err ) {
          cerr << err.what() << '\n';
      }
      system( "pause" );
      return 0;
  
  }//main()
  
  

   

3. String streams, cont.

• String streams are very useful for

  • formatting a string that contains structured data, e.g. HTML, XML, or SQL:

    
        SELECT product_code, description, price 
        FROM   table_products
        WHERE  product_code = 'BOOK'
        AND    price < 60.50
    
    

  • extracting typed objects out of a string:

    
        int string_2_int( string str )
        {
            int value;
            istringstream iss( str );
            iss >> value;
            return value;
        }
    
    

   

4. String stream example

• 
      #include <cassert>
      #include <string> 
      #include <sstream> 
      int main()
      {
          const double PI = 3.1415926;
          double value;
          std::stringstream  buffer;  // text buffer
          buffer.precision( 8 );      // increase default precision (*)
          buffer << PI;               // formatted output  
          buffer >> value;            // formatted input
          assert( PI == value );
          std::string text; 
          text = buffer.str( );  // returns std::string  
          buffer.str( "" );      // clear buffer  
          return 0;
      }
  
  

  (*) try commenting out precision change and see what happens

   

5. Unformatted I/O using String Stream

• 
      #include <cassert>
      #include <iostream>
      #include <sstream>
      using namespace std;
      int main()
      {
          stringstream buffer;
          int onechar; // because char cannot represent EOF
          cout << "Enter some text: ";
          while ( ( onechar = cin.get() ) != EOF ) {
              if ( onechar == '\n' ) {
                  break; // exit loop at the end of the line
  
              } else if ( isalpha( onechar ) ) {
                  buffer << "alpha: " << char( onechar ) << '\t' << onechar <<'\n';
  
              } else if ( isdigit( onechar ) ) {
                  buffer << "digit: " << char( onechar ) << '\t' << onechar <<'\n';
  
              } else {
                  buffer << "other: " << char( onechar ) << '\t' << onechar <<'\n';
              }
          }
          cout << buffer.str() << '\n'; // str() returns string
          return 0;
      }
  
  

   

6. Stream Functionality

7. Credits

• This handout is using material from Programming -- Principles and Practice Using C++

• About the author: Bjarne Stroustrup's homepage