The isalpha function

The Standard specifies that the set of letters, in the default locale, comprises the 26 upper-case and 26 lower-case letters of the Latin (English) alphabet. This set may vary in a locale-specific fashion (that is, under control of the setlocale function, .4) so long as

• isupper(c) implies isalpha(c)
• islower(c) implies isalpha(c)
• isspace(c), ispunct(c), iscntrl(c), or isdigit(c) implies !isalpha(c)

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