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

• The C Run-time Library (CRT) included with: - Microsoft Visual C++, 32-bit Edition, versions 4.0, 4.1, 4.2, 5.0

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());
   }

Keywords          : CPPIss
Version           : 4.0
Platform          : NT WINDOWS
Issue type        : kbprb