isalpha

int isalpha( int ch );

Checks if the given character is an alphabetic character, i.e. either an uppercase letter (ABCDEFGHIJKLMNOPQRSTUVWXYZ), or a lowercase letter (abcdefghijklmnopqrstuvwxyz).

In locales other than "C", an alphabetic character is a character for which isupper() or islower() returns true or any other character considered alphabetic by the locale. In any case, iscntrl(), isdigit(), ispunct() and isspace() will return false for this character.

The behavior is undefined if the value of ch is not representable as unsigned char and is not equal to EOF.

Parameters

Return value

Non-zero value if the character is an alphabetic character, zero otherwise.

Example

#include <ctype.h>
#include <stdio.h>
#include <locale.h>
 
int main(void)
{
    unsigned char c = '\xdf'; // German letter ß in ISO-8859-1
 
    printf("isalpha('\\xdf') in default C locale returned %d\n", !!isalpha(c));
 
    setlocale(LC_CTYPE, "de_DE.iso88591");
    printf("isalpha('\\xdf') in ISO-8859-1 locale returned %d\n", !!isalpha(c));
}

isalpha('\xdf') in default C locale returned 0
isalpha('\xdf') in ISO-8859-1 locale returned 1

References

• C17 standard (ISO/IEC 9899:2018):
• 7.4.1.2 The isalpha function (p: 145)
• C11 standard (ISO/IEC 9899:2011):
• 7.4.1.2 The isalpha function (p: 200-201)
• C99 standard (ISO/IEC 9899:1999):
• 7.4.1.2 The isalpha function (p: 181-182)
• C89/C90 standard (ISO/IEC 9899:1990):
• 4.3.1.2 The isalpha function

See also