7.4.1.2 The isalpha function

Synopsis

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#include <ctype.h>
int isalpha(int c);

Description

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The isalpha function tests for any character for which isupper or islower is true, or any character that is one of a locale-specific set of alphabetic characters for which none of iscntrl, isdigit, ispunct, or isspace is true.[1] In the “C” locale, isalpha returns true only for the characters for which isupper or islower is true.

Footnotes

[1]

The functions islower and isupper test true or false separately for each of these additional characters; all four combinations are possible.