DOCUMENT:Q246934  30-JUL-2001  [visualc]
TITLE   :BUG: istream::readsome Does Not Read Correctly on File Stream
PRODUCT :Microsoft C Compiler
PROD/VER:
OPER/SYS:
KEYWORDS:

======================================================================
SYMPTOMS
========

The istream::readsome function does not read correct data from a file.

CAUSE
=====

The basic_istream::readsome function has some limitations when used on certain
streams. Moreover, the MSDN documentation for basic_istream::readsome states
that internally basic_istream::readsome calls the read function. However, in the
basic_istream::readsome implementation, the read function is never called.

RESOLUTION
==========

Give preference to basic_istream::read.

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article.

MORE INFORMATION
================

Here is a code sample that illustrates the problem and provides a workaround:

   #include <iostream>
   #include <fstream>

   using namespace std;

   int main()
   {
   	ifstream file("c:\\config.sys",ios::in|ios::binary);

   	static char buffer[10];
   	buffer[10] = 0;

   	if ( !file )
   		cout << "unable to open file" << endl;
   	else
   	{
   		file.readsome(buffer,10); // It does not work properly.
   		//file.read( buffer, 10 ); // Uncomment this line for work around.
   		cout << buffer << endl;

   		cout << endl << "File contents are:" << endl;
   		file.seekg( 0 );	// Rewind file.
   		while( file.good() )
   		{
   			file.getline( buffer, 10 );
   			cout << buffer << endl;
   		}
   	}
   	return 0;
   }

Additional query words: stl

======================================================================
Keywords          :  
Issue type        : kbbug

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS
PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND.  MICROSOFT DISCLAIMS
ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES
OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  IN NO
EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR
ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL,
CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF
MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.  SOME STATES DO NOT ALLOW THE EXCLUSION
OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES
SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 2001.