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- size of a bit-field member of a structure
- size of an array (except in the case of variable length arrays)
- value of an enumeration constant
- value of a
caseconstant
#define:
- operates at compile time
- consumes no memory (though this is not too important)
- can use in compile-time constant expression
- uses different syntax; can make mistake with ;
- can't create pointers to
- no type checking
const:
- operates at run time
- consumes memory (though this is not too important)
- can't use in compile-time constant expression
- uses consistent syntax
- can create pointers to
- does type checking
If any of these are required, then an integer constant (which would be an rvalue) must be used.
Method | Evaluated at | Consumes Memory | Viewable by Debuggers | Type Checking | Compile-time constant expression |
|---|---|---|---|---|---|
Enumerations | compile time | no | yes | yes | no |
| run time | yes | yes | yes | no |
Macros | preprocessor | no | no | no | yes |
This recommendation is related to EXP07-A. Do not diminish the benefits of constants by assuming their values in expressions.
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Search for vulnerabilities resulting from the violation of this rule on the CERT website.
References
| Wiki Markup |
|---|
\[[Summit 05|AA. C References#Summit 05]\] [Question 10.5b|http://c-faq.com/cpp/constvsdefine.html]
\[[ISO/IEC 9899-1999|AA. C References#ISO/IEC 9899-1999]\] Section 6.3.2.1, "Lvalues, arrays, and function designators," Section 6.7.2.2, "Enumeration specifiers," and Section 6.10.3, "Macro replacement" |
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