PRB: istream::seekg() Does Not Reset EOF State

• The C/C++ Compiler (CL.EXE), included with:
  • Microsoft Visual C++, 32-bit Editions, versions 4.0, 4.1, 4.2, 5.0, 6.0

SYMPTOMS

The istream::seekg() function does not reset the EOF (end of file) state when the stream pointer is already at EOF.

RESOLUTION

To work around this problem, call ios::clear() for the stream before calling istream::seekg().

STATUS

This behavior is by design.

MORE INFORMATION

You don't need to call clear(), if the stream pointer is not already at EOF.

Sample Code

/* Compile options needed: None
*/ 

// Input: A file with the name test.txt containing some characters.

#include <fstream.h>
#include <assert.h>

void main()
{
  fstream in("test.txt", ios::in);

  char c;
  int i = 0;

  // Count characters in file
  while (in.get(c))
     ++i;

  assert(in.eof());

  // Reset read pointer to beginning of file
  in.clear();
  in.seekg(0, ios::beg);

  // Check that file can now be read.
  // Fails without the in.clear() statement above.
  assert(!in.eof());
} 

Additional query words:

Keywords : kbCompiler kbCPPonly kbVC kbVC400 kbVC410 kbVC420 kbVC500 kbVC600
Version : 4.0
Platform : NT WINDOWS
Issue type : kbprb