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Avoid the use of magic numbers in code when possible. Magic numbers are constant values that represent either an arbitrary value (such as a determined appropriate buffer size, ) or a malleable concept (such as the age a person is considered an adult, which could change between geopolitical boundaries). Rather, use appropriately named symbolic constants to clarify the intent of the code. In addition, if a specific value needs to be changed, reassigning a symbolic constant once is more efficient and less error prone then than replacing every instance of the value to be changed.

Non-Compliant Code Example

The meaning of the numeric literal 18 is not clear in this example.

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The compliant solution replaces 18 with the symbolic constant ADULT_AGE to clarify the meaning of the code.

Wiki MarkupWhen declaring immutable symbolic values, such as {{ADULT_AGE}} , it is best to declare them as a constant in accordance with \[[DCL00-A. Declare immutable values using enum or const]\].

enum { ADULT_AGE=18 };
/* ... */
if (age >= ADULT_AGE) {
   /* Take action */
}
else {
  /* Take a different action */
}
/* ... */

Exceptions

DCL06-EX1: While replacing numeric constants with a symbolic constant is often a good practice, it can be taken too far. Exceptions can be made for constants that are themselves the abstraction you want to represent, as in this compliant solution.

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When implementing recommendations, it is always necessary to use sound judgment.

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Search for vulnerabilities resulting from the violation of this rule on the CERT website.

References

\[[Henricson 1992|AA. C References#Henricson 1992]\] Chapter 10, "[Constants|http://www.doc.ic.ac.uk/lab/cplus/c++.rules/chap10.html]"
\[[ISO/IEC 9899-1999|AA. C References#ISO/IEC 9899-1999]\] Section 6.7, "Declarations"

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