According to the C Standard, 7.4.1 paragraph 1 [ISO/IEC 9899:20112024],
The header
<ctype.h>
declares several functions useful for classifying and mapping characters. In all cases the argument is anint
, the value of which shall be representable as anunsigned char
or shall equal the value of the macroEOF
. If the argument has any other value, the behavior is undefined.
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Bibliography
[ISO/IEC 9899:20112024] | 7.4.1, "Character Handling <ctype.h >" |
[Kettlewell 2002] | Section 1.1, "<ctype.h > and Characters Types" |
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