[previous] MISRA-C:2004  Rule  9.3:  (Required) [next] In an enumerator list, the '=' construct shall not be used to explicitly initialise members other than the first, unless all items are explicitly initialised.
If an enumerator list is given with no explicit initialisation of members, then C allocates a sequence of integers starting at 0 for the first element and increasing by 1 for each subsequent element.

An explicit initialisation of the first element, as permitted by the above rule, forces the allocation of integers to start at the given value. When adopting this approach it is essential to ensure that the initialisation value used is small enough that no subsequent value in the list will exceed the int storage used by enumeration constants.

Explicit initialisation of all items in the list, which is also permissible, prevents the mixing of automatic and manual allocation, which is error prone. However it is then the responsibility of the programmer to ensure that all values are in the required range, and that values are not unintentionally duplicated. 

enum colour { red=3, blue, green, yellow=5 };     /* non compliant */
/* green and yellow represent the same value - this is duplication */

enum colour { red=3, blue=4, green=5, yellow=5 };     /* compliant */
/* green and yellow represent the same value - this is duplication */

QAC messages that encompass this guideline:

0723 Initialize none, first only, or all entries in this enumerator list.


(c) The Motor Industry Research Association, 2004
QA C Source Code Analyser 8.1.2
MISRA-C:2004 Compliance Module 3.2
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