Q67273: Error in Installation Manual for bounds-error() Routine

Article: Q67273
Product(s): See article
Version(s): 6.00   | 6.00
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | docerr | mspl13_c
Last Modified: 4-DEC-1990

Page 58 of the Microsoft C "Installing and Using the Professional
Development System" manual is unclear when stating that the program
example will overwrite bounds and CodeView will catch that error. The
program returns the following run-time error upon exiting the
bounds_error routine, rather than when the error actually took place:

   run-time error R6012
   - illegal near-pointer use

The manual states:

   The program runs until it reaches the "for" statement in the
   "bounds_error" function, where the array bounds are exceeded. The
   output window reports an error while a CodeView dialog box
   indicates the program has terminated.

This statement implies that the program will fail when the bounds of
the array are exceeded, which is not entirely true.

The program will indeed fail in this case because the array bounds are
exceeded, overwriting stack information in the process. However, the
program will not fail until *after* the for loop when the
bounds_error() function terminates. At that time, the pointer check
function will determine that the stack has been overwritten and will
issue the error message above.

If the array had not been stack based (that is, global or static) and
the stack data had not been trashed, the program would not have
failed. However, important data may still have been lost. To trap
overwrite errors of this nature, you could use "Bounds Checker" by
Nu-Mega.

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

void bounds_error(void)
{
   int loop, the_num[10];
   for(loop=0;loop<15;loop++)
      the_num[loop]=loop;
}
void main(void)
{
   bounds_error();
}

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