Q61314: INFO: The Limit of Macro Expansion

Article: Q61314
Product(s): Microsoft C Compiler
Version(s): 1.0,1.5,1.51,2.0,2.1,5.1,6.0,6.0a,6.0ax
Operating System(s): 
Keyword(s): kbCompiler
Last Modified: 25-JUL-2001

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The information in this article applies to:

- Microsoft C/C++ Compiler (CL.EXE), included with:
   - Microsoft C for MS-DOS, versions 6.0, 6.0a, 6.0ax 
   - Microsoft C for OS/2, versions 5.1, 6.0, 6.0a 
   - Microsoft C/C++ for MS-DOS, version 7.0 
   - Microsoft Visual C++, versions 1.0, 1.5, 1.51 
   - *EDITOR Please do not choose this product*Microsoft Visual C++ 32-bit Edition* use 241, 265, 225, versions 1.0, 2.0, 2.1 
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SUMMARY
=======

In Microsoft C and Visual C++, the limit of a preprocessor macro expansion can
be no more than 6K when it is FULLY expanded. Similarly, actual arguments plus
FULLY expanded actual arguments are not allowed to exceed 6K during a single
macro expansion. Note that this is not the same as saying that the macro
DEFINITIONS must be 6K or less. The 6K limitation was chosen because the buffer
used for expansion is dynamically allocated, and 6K seems to be a reasonable
limit for most real programs.

Additionally, there is a nesting DEPTH limit in C versions 6.0 and below of 64 on
macros in C1.EXE, and 256 in C1L.EXE. The nesting limit for C 7.0 and Visual C++
1.0 is 255. This may be noticed only if you are writing macros for some
relocatable indexing scheme, such as in the following example:

     #define INCOME 1;
     #define EXPENSE (INCOME+1)
     #define GINCOME (EXPENSE+1)
     #define TAXES (GINCOME+1)
     #define NINCOME (TAXES+1)

and so on.

Additional query words: 8.00 8.00c 9.00 9.10

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Keywords          : kbCompiler 
Technology        : kbVCsearch kbAudDeveloper kbCVCComp
Version           : :1.0,1.5,1.51,2.0,2.1,5.1,6.0,6.0a,6.0ax
Issue type        : kbinfo

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