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From "Martin Sebor (JIRA)" <>
Subject [jira] Created: (STDCXX-241) std::istream::seekg problem (LWG issue 136)
Date Wed, 28 Jun 2006 20:45:33 GMT
std::istream::seekg problem (LWG issue 136)

         Key: STDCXX-241
     Project: C++ Standard Library
        Type: Bug

  Components: 27. Input/Output  
    Versions: 4.1.2, 4.1.3    
 Environment: all
    Reporter: Martin Sebor

Moved from the Rogue Wave bug tracking database:

Fix Priority: Must Fix
Long Description: 
  *** Nov 10 1999 9:33PM *** sebor ***

Problem: seekg - problem

see seek2.cpp:

The ANSI/ISO-C++ document(ISO/IEC 14882:1998(E)) states about the effects of seekg:

ANSI> Effects: If fail() != true, executes rdbuf()í>pubseekpos( pos).

(The RW-Implementation instead executes rdbuf()->pubseekpos(pos, ios_base::in);)
pubseekpos calls seekpos which is declared:

pos_type seekpos(pos_type sp, ios_base::openmode which
                  = ios_base::in | ios_base::out);

since the 2nd Argument (which) is not given in the above call of pubseekpos
the value of the which-Argument is the default value ios_base::in | ios_base::out.
seekpos should alter both the position in the input and the output sequence in this case.
The RW-Implementation alters only the position in the input-sequence.

Though the RW-implementation seems to be intuitivly right, it is formally
not conforming.
I think RogueWave should support the lwg issue No 136 described in


#include <string>
#include <sstream>
#include <iostream>

using namespace std;

typedef basic_stringbuf<char, char_traits<char>, allocator<char> > buffer;
typedef basic_istream<char, char_traits<char> > input_stream;
typedef char_traits <char> traits;
typedef char_traits<char>::pos_type pos_type;

#define VERIFY(p1,p2) verify(p1,p2,__LINE__)

template <class T> void verify (T p1, T p2, int line)
  if(p1 != p2) {
    cerr << "line " << line << ": " << p1 << " should be " 
         << p2 << '\n';

template <> void verify (string p1, string p2, int line)
  if(p1 != p2) {
    cerr << "line " << line << ": \"" << p1 << "\" should be
         << p2 << "\" \n";

int main()
  const string expstr ("Rogue Wave");
  buffer  buf (expstr, ios_base::in | ios_base::out);
  typedef basic_iostream<char, char_traits<char> > iostrm; 
  iostrm  iostobj(&buf);
  char s[80];
  VERIFY ((void *)iostobj.rdbuf(),(void *)&buf);
  VERIFY (iostobj.gcount(),streamsize(0));
  iostobj >> s;
  VERIFY (string(s), string("Rogue"));
  iostobj.get (s, sizeof s);
  VERIFY (string(s), string(" Wave"));
  iostobj.clear ();
  iostobj.seekg (0, ios::end);
  iostobj.write (" Software", 9);
  iostobj.seekp (0);
  iostobj.get (s, sizeof s);
  iostobj.clear ();
  VERIFY (string(s), string("Rogue Wave Software"));
CC -c -mt -D_RWSTD_USE_CONFIG -I/amd/devco/sebor/dev/stdlib/include -I/build/seb
or/sunpro-5.8.j1-12d/include -I/amd/devco/sebor/dev/stdlib/examples/include  -li
brary=%none -O  +w  t.cpp
CC t.o -o t -library=%none -L/build/sebor/sunpro-5.8.j1-12d/lib  -mt  -L/build/s
ebor/sunpro-5.8.j1-12d/lib -lstd12d   -lm
line 55: " Software" should be "Rogue Wave Software" 

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