Q58427: PRB: Changing STDIN Translation Mode from Text to Binary

Article: Q58427
Product(s): Microsoft C Compiler
Version(s): winnt:
Operating System(s): 
Keyword(s): kbCRT kbVC kbprb
Last Modified: 25-JUL-2001

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The information in this article applies to:

- The C Run-Time (CRT), included with:
   - Microsoft C for MS-DOS, versions 5.1, 6.0, 6.0a, 6.0ax 
   - Microsoft C/C++ for MS-DOS, version 7.0 
   - Microsoft Visual C++, versions 1.0, 1.50 
   - *EDITOR Please do not choose this product*Microsoft Visual C++ 32-bit Edition* use 241, 265, 225, versions 1.0, 2.0 
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SYMPTOMS
========


In Microsoft C, when a ^Z (CTRL+Z) is entered as part of a string input in
response to gets() or scanf(), the next line does not prompt for an input.

CAUSE
=====

Because STDIN is a predefined file pointer opened in text mode, and a ^Z
character is an end-of-file marker in MS-DOS, the ^Z character automatically
closes the file pointer. The gets() or scanf() function does not stop to accept
input from STDIN following the previous input containing a ^Z character.

RESOLUTION
==========

To work around this problem, change the translation mode of STDIN from text mode
to binary mode. Because the ^Z character is not translated as an end-of-file
character in binary mode, the gets() from the following example accepts input
only following a ^Z from STDIN after the translation.

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

To change STDIN from text mode to binary mode, use the setmode() run-time
function to change the translation mode. The following code demonstrates this
behavior, and includes the setmode() function to show how to change STDIN from
text mode to binary mode. Remove the comment delimiters to observe the
difference in the program's behavior after adding the setmode() function.

Sample Code
-----------

  /* Compile options needed: none
  */ 

  #include <stdio.h>
  #include <string.h>
  #include <fcntl.h>

  void main (void)
  {
     char str1[20];

  /* if( setmode ( fileno ( stdin ), O_BINARY ) == -1 )
            perror ( "Cannot set stdin to binary mode" );
     else
            printf ( "stdin mode successfully set to binary\n" );
  */ 
     do {
            printf ( "Enter a string : " );
            gets ( str1 );
     } while ( strcmp( str1,"n" && strcmp( str1, "\n\r") );

  }

Compile the above code and run the program. If you enter a string and then press
the ENTER key, the program will loop and prompt for another string. However, if
you enter a ^Z character, you will see that the program doesn't perform as you
would expect.

Now, uncomment the if-else clause. Recompile the program and run it. Input that
includes a ^Z character is now accepted without infinite looping.

Additional query words: 1.00 1.50 2.00 5.10 6.00 6.00a 6.00ax 7.00

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Keywords          : kbCRT kbVC kbprb 
Technology        : kbVCsearch kbAudDeveloper kbCRT
Version           : winnt:
Issue type        : kbprb

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