Q246934: BUG: istream::readsome Does Not Read Correctly on File Stream

Article: Q246934
Product(s): Microsoft C Compiler
Version(s): 
Operating System(s): 
Keyword(s): 
Last Modified: 30-JUL-2001

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

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