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This is recommended because the C99 standard requires only the digit characters ('0' - '9') to have consecutive numerical values C99 N1401. ThusConsequently, operations that rely on expected values for plain character or plain wide character-typed expressions can lead to unexpected behavior.
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This noncompliant code example attempts to determine if the value of a character variable is between 'a' and 'c' inclusive. However, since because the C99 standard does not require the letter characters to be consecutive or in alphabetical order, the check might not work as expected.
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| Code Block | ||||
|---|---|---|---|---|
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char ch = 't';
if ((ch == 'a') || (ch == 'b') || (ch == 'c')) {
/* ... */
}
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Exceptions
STR09-EX1EX0: Consecutive values for characters like a~z can be assumed on platforms where ASCII or Unicode is used. This recommendation is primarily concerned with platform portability, for example, if code is migrated from ASCII systems to non-ASCII systems.
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