From: Alex Vinokur <alexvn AT bigfoot DOT com>
Newsgroups: comp.os.msdos.djgpp,comp.lang.c++
Subject: whitespaces & strstream
Followup-To: comp.lang.c++
Date: Sun, 16 Sep 2001 13:49:07 +0200
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=========================================================
GNU C++ version 2.95.3 20010315/djgpp (release) (djgpp)
compiled by GNU C version 2.95.3 20010315/djgpp (release)
Windows98
=========================================================

Here is a program, results of the running and several questions.

###### Source file ######
#include <string>
#include <strstream>


//-------------------------------------
int main ()
{
string  init_str,
  from1,
  to1,
  from2,
  to2,
  from3,
  to3,
  from4,
  to4;
strstream       tmp_ss1,
  tmp_ss2,
  tmp_ss3,
  tmp_ss4;
bool  rc_bool;


  init_str = "      ";

  //-------------------------
  cout << endl;
  cout << "   === Test#1 ===" << endl;
  from1 = init_str;
  tmp_ss1.setf (ios::skipws);
  tmp_ss1 << from1;
  tmp_ss1 << ends;
  to1 = tmp_ss1.str();

  cout << "tmp_ss1 : in_avail = "
       << tmp_ss1.rdbuf()->in_avail()
       << from1
       << endl;

  tmp_ss1.rdbuf()->freeze (0);

  cout << "from1 = <" << from1 << ">" << endl;
  cout << "to1 = <" << to1 << ">" << endl;
  cout << ((from1 == to1) ? "OK : from1 == to1" : "FAILURE : from1 !=
to1") << endl;


  //-------------------------
  cout << endl;
  cout << "   === Test#2 ===" << endl;
  from2 = init_str;
  tmp_ss2.unsetf (ios::skipws);
  tmp_ss2 << from2;
  tmp_ss2 << ends;
  to2 = tmp_ss2.str();

  cout << "tmp_ss2 : in_avail = "
       << tmp_ss2.rdbuf()->in_avail()
       << from2
       << endl;

  tmp_ss2.rdbuf()->freeze (0);

  cout << "from2 = <" << from2 << ">" << endl;
  cout << "to2 = <" << to2 << ">" << endl;
  cout << ((from2 == to2) ? "OK : from2 == to2" : "FAILURE : from2 !=
to2") << endl;

  //-------------------------
  cout << endl;
  cout << "   === Test#3 ===" << endl;
  from3 = init_str;
  tmp_ss3.setf (ios::skipws);
  tmp_ss3 << from3;
  tmp_ss3 << ends;
  rc_bool = (tmp_ss3 >> to3);

  cout << "tmp_ss3 : in_avail = "
       << tmp_ss3.rdbuf()->in_avail()
       << from3
       << endl;

  tmp_ss3.rdbuf()->freeze (0);

  cout << "from3 = <" << from3 << ">" << endl;
  if (rc_bool) cout << "to3 = <" << to3 << ">" << endl;
  else  cout << "to3 : Cannot get" << endl;
  cout << ((from3 == to3) ? "OK : from3 == to3" : "FAILURE : from3 !=
to3") << endl;

  //-------------------------
  cout << endl;
  cout << "   === Test#4 ===" << endl;
  from4 = init_str;
  tmp_ss4.unsetf (ios::skipws);
  tmp_ss4 << from4;
  tmp_ss4 << ends;
  rc_bool = (tmp_ss4 >> to4);

  cout << "tmp_ss4 : in_avail = "
       << tmp_ss4.rdbuf()->in_avail()
       << from4
       << endl;
  tmp_ss4.rdbuf()->freeze (0);

  cout << "from4 = <" << from4 << ">" << endl;
  if (rc_bool) cout << "to4 = <" << to4 << ">" << endl;
  else  cout << "to4 : Cannot get" << endl;
  cout << ((from4 == to4) ? "OK : from4 == to4" : "FAILURE : from4 !=
to4") << endl;

  return 4;
}


#########################


######## Running ########

   === Test#1 ===
tmp_ss1 : in_avail = 1
from1 = <      >
to1 = <      >
OK : from1 == to1

   === Test#2 ===
tmp_ss2 : in_avail = 1
from2 = <      >
to2 = <      >
OK : from2 == to2

   === Test#3 ===
tmp_ss3 : in_avail = 0
from3 = <      >
to3 = < >
FAILURE : from3 != to3

   === Test#4 ===
tmp_ss4 : in_avail = 1
from4 = <      >
to4 : Cannot get
FAILURE : from4 != to4


#########################



Questions.
  #1. Test#1 contains tmp_ss1.setf (ios::skipws).
      Test#2 contains tmp_ss2.unsetf (ios::skipws).
      In spite of that both test#1 and test#2
        produce the same OK-result.
      Why?

  #2. Both test#3 and test#4 produce FAILURE-result.
      Why?
      Can we get OK-result using the clause
      tmp_ss >> to; [ NOT : to = tmp_ss.str(); ] ?


  ===========================
  Alex Vinokur
    mailto:alexvn AT bigfoot DOT com
    mailto:alexvn AT dr DOT com
    http://up.to/alexvn
    http://go.to/alexv_math
  ===========================