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When used in program logic, literals can reduce the readability of source code.  As a result, literals in general, and integer constants in particular, are frequently called _magic numbers_ because their purpose is often obscured. Magic numbers may be 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 can change between geopolitical boundaries). Rather than embed literals in program logic, 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 than replacing every instance of the value \[[Saks 02|AA. C References#Saks 02]\].

{{const}}\-qualified objects are likely to incur some runtime overhead  \[[Saks 01b|AA. C References#Saks 02]\]. Most C compilers, for example, allocate memory for {{const}}\-qualified objects. {{const}}\-qualified objects declared inside a function body may have automatic storage duration. If so, the compiler will allocate storage for the object, and it will be on the stack. As a result, this storage will need to be allocated and initialized each time the containing function is invoked.

defines an _object-like_ macro that causes each subsequent instance of the macro name to be replaced by the replacement list of preprocessing tokens that constitute the remainder of the directive \[[ISO/IEC 9899:1999|AA. C References#ISO/IEC 9899-1999]\].

Using the {{sizeof}} expression in this example reduces the total number of names declared in the program, which is generally a good idea \[[Saks 02|AA. C References#Saks 02]\].  The {{sizeof}} operator is almost always evaluated at compile time (except in the case of variable-length arrays).

\[[Henricson 92|AA. C References#Henricson 92]\] 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 6.3.2.1, "Lvalues, arrays, and function designators," Section 6.7, "Declarations," Section 6.7.2.2, "Enumeration specifiers," and Section 6.10.3, "Macro replacement"
\[[ISO/IEC PDTR 24772|AA. C References#ISO/IEC PDTR 24772]\] "BRS Leveraging human experience"
\[[MITRE 07|AA. C References#MITRE 07]\] [CWE ID 547|http://cwe.mitre.org/data/definitions/547.html], "Use of Hard-coded, Security-relevant Constants"
\[[Saks 01a|AA. C References#Saks 01]\]
\[[Saks 01b|AA. C References#Saks 02]\]
\[[Saks 02|AA. C References#Saks 02]\]
\[[Summit 05|AA. C References#Summit 05]\] [Question 10.5b|http://c-faq.com/cpp/constvsdefine.html]