Stringstreams in C++ 

Teilnehmerfrage Wie Text in Wörter zerlegen?

#include <iostream> /* ::std::cout         */
#include <ostream>  /* <<                  */
#include <string>   /* <<                  */
#include <sstream>
int main()
{ ::std::stringstream source;
  source << "alpha beta gamma";
  ::std::string word;
  while( source >> word )::std::cout << word << '\n'; }

Main.java

#include <iostream>
#include <ostream>
#include <string>
#include <iterator>
#include <algorithm>
#include <vector>
#include <initializer_list>
#include <sstream>
int main() 
{ ::std::string const source = "Haus Hof Haus Haus Garten";
  ::std::stringstream stream( source );
  ::std::vector<::std::string> words
  ( std::istream_iterator<std::string>{ stream }, 
    std::istream_iterator<std::string>{} );
  ::std::sort( ::std::begin( words ), ::std::end( words ) );
  ::std::unique_copy
  ( ::std::begin( words ), ::std::end( words), 
    ::std::ostream_iterator< ::std::string >( ::std::cout, "\n" ) );}
Garten
Haus
Hof

Beispiel

text mit Zeilen der Form

a=b

interpretieren

std::istringstream istringstream_object( text );
std::string line;
while( std::getline(istringstream_object, line).good() )
{ auto start_of_line_position = begin( line );
  auto end_of_line_position = end( line );
  auto equal_sign_position = find( start_of_line_position, end_of_line_position, '=' );
  std::string const keyword( start_of_line_position, equal_sign_position );
  auto value_position = start_of_line_position != end_of_line_position ? equal_sign_position + 1 : equal_sign_position;  
  std::string value(value_position, end_of_line_position); }

Abschnitt Einlesen mit getline

getline liest normalerweise eine Zeile ein.

#include <iostream>
#include <ostream>
#include <string>
int main() 
{ ::std::string str;
  getline( ::std::cin, str );
  ::std::cout << str << '\n'; }
::std::cout
1
1

Es kann aber auch ein andere Separator als weiteres drittes Argument von getline angegeben werden. Das folgende Programm addiert plusseparierte Zahlen jeder Zeile. (Allerdings ohne Behandlung von Eingabefehlern.)

#include <iostream>
#include <ostream>
#include <string>
#include <sstream>
int main() 
{ for( ::std::string input; getline( ::std::cin, input ); )
  { ::std::stringstream source; source << input; 
    int sum = 0; 
    while( getline( source, input, '+' ))sum += ::std::stoi( input ); 
    ::std::cout << sum << '\n'; }}
2+3
5
1+22+333+4444
4800

Problemlösung fehlende to_string-Funktion

#include <iostream>
#include <ostream>
#include <sstream>
#include <initializer_list> 
template< typename V >std::string to_string( V v )
{ ::std::stringstream s; s << v; return s.str(); }
int main()
{ auto s = to_string( 22 ); ::std::cout << s + "a" << '\n';  }

Automatisches Formatieren von Tabellen

main.cpp

#include <sstream>
#include <iomanip>
#include <vector>
#include <algorithm>
#include <iostream>
#include <ostream>
static ::std::string align_columns( ::std::string const & str )
{ /* Based on code posted to comp.lang.c++ by Ben Bacarisse in 2017*/
  ::std::vector< ::std::string::size_type >widths;
  ::std::istringstream is( str );
  ::std::string word;
  { unsigned col = 0;
    while( is >> word )
    { ::std::clog << "read \"" << word << "\".\n";
      if( col >= widths.size() )
      widths.push_back( word.length() );
      else widths[ col ]= ::std::max( widths[ col ], word.length() );
      ::std::clog << "peek is \"" <<( is.peek()== '\n' ? "\\n" : " " )<< "\".\n";
      col = is.peek() == '\n' ? 0 : col + 1; }}
  is.clear();
  is.seekg( 0 );
  std::ostringstream os;
  os << ::std::left;
  { unsigned col = 0;
    while( is >> word )
    { os << 
      ::std::setw( static_cast< int >( widths[ col ]))<< 
      word << 
      static_cast< char >( is.peek() );
      col = is.peek() == '\n' ? 0 : col + 1; }}
  
  return os.str(); }
int main()
{ std::string source = R"(
  Alpha Beta
  Epsilon Eta
  )";
  ::std::cout << align_columns( source ); }

transcript

Alpha   Beta
Epsilon Eta 
read "Alpha".
peek is "32".
read "Beta".
peek is "10".
read "Epsilon".
peek is "32".
read "Eta".
peek is "10".

main.cpp

#include <sstream>
#include <iomanip>
#include <vector>
#include <algorithm>
static ::std::string align_columns( ::std::string const & str )
{ /* Based on code by Ben Bacarisse posted to comp.lang.c++ in 2017 */
  ::std::vector< ::std::string::size_type >widths;
  ::std::istringstream is( str );
  ::std::string word;
  { unsigned col = 0;
    while( is >> word )
    { if( col >= widths.size() )
      widths.push_back( word.length() );
      else widths[ col ]= ::std::max( widths[ col ], word.length() );
      col = is.peek() == '\n' ? 0 : col + 1; }}
  is.clear();
  is.seekg( 0 );
  std::ostringstream os;
  os << ::std::left;
  { unsigned col = 0;
    while( is >> word )
    { os << 
      ::std::setw( static_cast< int >( widths[ col ]))<< 
      word << 
      static_cast< char >( is.peek() );
      col = is.peek() == '\n' ? 0 : col + 1; }}
  
  return os.str(); }
#include <iostream>
int main()
{ std::string source = R"(
  Alpha Beta Gamma Delta Epsilon
  Zeta Eta Theta Iota Kappa
  Lambda My Ny Xi Omikron
  Pi Rho Sigma Tau Ypsilon
  Phi Chi Psi Omega
  )";
  ::std::cout << align_columns( source ); }

transcript

Alpha  Beta Gamma Delta Epsilon
Zeta   Eta  Theta Iota  Kappa  
Lambda My   Ny    Xi    Omikron
Pi     Rho  Sigma Tau   Ypsilon
Phi    Chi  Psi   Omega