Q22321: INFO: Common Programming Errors in the C Language

Article: Q22321
Product(s): Microsoft C Compiler
Version(s): 1.0,1.5,2.0,4.0,5.0,6.0
Operating System(s): 
Keyword(s): kbLangC kbVC100 kbVC150 kbVC200 kbVC400 kbVC500 kbVC600
Last Modified: 29-NOV-2001

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft C for MS-DOS 
- Microsoft C/C++ for MS-DOS 
- Microsoft Visual C++, versions 1.0, 1.5, 2.0, 4.0 
- Microsoft Visual C++, 32-bit Enterprise Edition, versions 5.0, 6.0 
- Microsoft Visual C++, 32-bit Professional Edition, versions 5.0, 6.0 
- Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
-------------------------------------------------------------------------------

SUMMARY
=======

The text below lists some of the most common errors that occur programming in
the C language. Any one of these items can cause unpredictable results, such as
invalid data. Some are caught by the compiler and reported as errors or
warnings.

- Using an automatic variable that has not been initialized

- Omitting a closing comment delimiter

- Using an array index greater than the length of the array (In C, array
  indexes run from zero to <length>-1.)

- Omitting a semicolon or a closing brace

- Using an uninitialized pointer

- Using a forward slash when a backslash is required (for example, substituting
  "/n" for "\n.")

- Using "=" in a comparison where "==" is desired

- Overwriting the null terminator for a string

- Prematurely terminating a function declaration with a semicolon (The compiler
  often flags the "orphan" block of code as a syntax error.)

- Specifying the values of variables in a scanf() statement instead of their
  addresses

- Failing to declare the return type for a function

- Assuming an expression evaluation order when using an expression with side
  effects (For example, a[i] = i++; is ambiguous and dangerous.)

- Failing to account that a static variable in a function is initialized only
  once

- Omitting a "break" from a case in a switch statement (Execution "falls
  through" to subsequent cases.)

- Using "break" to exit a block of code associated with an if statement (The
  break statement exits a block of code associated with a for, switch, or while
  statement.)

- Comparing a "char" variable against EOF (-1). The following idiom results in
  an infinite loop when char is unsigned. Note that char is signed by default,
  so the following will only fail when using the "/J" compiler option:

  char c;
  while ((c = getchar()) != EOF)
     {
     }

Additional query words:

======================================================================
Keywords          : kbLangC kbVC100 kbVC150 kbVC200 kbVC400 kbVC500 kbVC600 
Technology        : kbVCsearch kbVC400 kbAudDeveloper kbZNotKeyword8 kbvc150 kbvc100 kbCCompSearch kbZNotKeyword3 kbVC500 kbVC600 kbVC200 kbVC32bitSearch kbVC500Search
Version           : :1.0,1.5,2.0,4.0,5.0,6.0
Issue type        : kbinfo

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1986-2002.