Q50732: INFO: Pointer to Undeclared Structure Does Not Generate Error

Article: Q50732
Product(s): Microsoft C Compiler
Version(s): 1.0,1.5,1.51,2.0,2.1,4.0,5.0,6.0
Operating System(s): 
Keyword(s): kbcode kbCompiler kbVC100 kbVC150 kbVC151 kbVC200 kbVC210 kbVC400 kbVC500 kbVC600
Last Modified: 29-NOV-2001

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The information in this article applies to:

- Microsoft C for MS-DOS 
- Microsoft C for OS/2 
- Microsoft C/C++ for MS-DOS 
- Microsoft Visual C++ for Windows, 16-bit edition, versions 1.0, 1.5, 1.51 
- Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 2.1, 4.0, 5.0, 6.0 
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SUMMARY
=======

Code that declares a pointer to a nonexistent structure compiles without warning
or error. This is correct behavior.

Note that dereferencing a pointer to an undefined structure, or attempting to use
a field, will produce errors. In general, you are allowed to make a reference to
an undefined struct as long as the operation doesn't need to know the size of
that struct or the names of its fields. This method of declaration is commonly
used in linked lists.

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

     void main (void)
     {
        struct non_existent *ptr;         // legal
        struct x
        {
         struct x *previous;      // legal, note that struct x is
         struct x *next;          // not yet defined
        };
     }

Additional query words: 8.00

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Keywords          : kbcode kbCompiler kbVC100 kbVC150 kbVC151 kbVC200 kbVC210 kbVC400 kbVC500 kbVC600 
Technology        : kbVCsearch kbVC400 kbAudDeveloper kbZNotKeyword8 kbvc150 kbvc100 kbCCompSearch kbZNotKeyword3 kbVC500 kbVC600 kbVC151 kbVC200 kbVC210 kbVC32bitSearch kbVC16bitSearch kbVC500Search
Version           : :1.0,1.5,1.51,2.0,2.1,4.0,5.0,6.0
Issue type        : kbinfo

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