Anonymous

include <stdio.h>
#include <stdlib.h>

#include <sstream>

main() {

  std::stringstream mystr;

  printf("string='%s'\n",mystr.str().c_str() );
  mystr << "bla";
  printf("string='%s'\n",mystr.str().c_str() );
  mystr.str("abcd");
  printf("string='%s'\n",mystr.str().c_str() );
  mystr << "bla2" << "bla3";
  printf("string='%s'\n",mystr.str().c_str() );
  mystr << "bla4" << "bla5";
  printf("string='%s'\n",mystr.str().c_str() );
}

Output of the application:
string=''
string='bla'
string='abcd'
string='bla2bla3'
string='bla2bla3bla4bla5'