isalnum

C

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Program utilities

Variadic function support

Error handling

Dynamic memory management

Date and time utilities

Strings library

Algorithms

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Input/output support

Localization support

Atomic operations (C11)

Thread support (C11)

Technical Specifications

Strings library

Byte strings

Multibyte strings

Wide strings

Null-terminated byte strings

Functions
Character manipulation
isalnum isalpha islower isupper isdigit isxdigit isblank (C99)	iscntrl isgraph isspace isprint ispunct tolower toupper
Conversions to numeric formats
atof atoiatolatoll (C99) strtolstrtoll (C99)	strtoulstrtoull (C99) strtofstrtodstrtold (C99)(C99) strtoimaxstrtoumax (C99)(C99)
String manipulation
strcpystrcpy_s (C11)
strncpystrncpy_s (C11)
strcatstrcat_s (C11)
strncatstrncat_s (C11)
strxfrm
String examination
strlenstrnlen_s (C11) strcmp strncmp strcoll strchr strrchr	strspn strcspn strpbrk strstr strtokstrtok_s (C11)
Memory manipulation
memchr
memcmp
memsetmemset_s (C11)
memcpymemcpy_s (C11)
memmovememmove_s (C11)
Miscellaneous
strerrorstrerror_sstrerrorlen_s (C11)(C11)

Defined in header <ctype.h>
int isalnum( int ch );

Checks if the given character is an alphanumeric character as classified by the current C locale. In the default locale, the following characters are alphanumeric:

• digits (0123456789)
• uppercase letters (ABCDEFGHIJKLMNOPQRSTUVWXYZ)
• lowercase letters (abcdefghijklmnopqrstuvwxyz)

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

Parameters

ch

-

character to classify

Return value

Non-zero value if the character is an alphanumeric character, 0 otherwise.

Example

Demonstrates the use of isalnum() with different locales (OS-specific).

Run this code

#include <stdio.h>
#include <ctype.h>
#include <locale.h>

int main(void)
{
    unsigned char c = '\xdf'; // German letter  in ISO-8859-1

    printf("isalnum('\\xdf') in default C locale returned%d\n", !!isalnum(c));

    if(setlocale(LC_CTYPE, "de_DE.iso88591"))
        printf("isalnum('\\xdf') in ISO-8859-1 locale returned%d\n", !!isalnum(c));
}

Possible output:

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

References

• C11 standard (ISO/IEC 9899:2011):

• 7.4.1.1 The isalnum function (p: 200)

• C99 standard (ISO/IEC 9899:1999):

• 7.4.1.1 The isalnum function (p: 181)

• C89/C90 standard (ISO/IEC 9899:1990):

• 4.3.1.1 The isalnum function

See also

iswalnum (C95)

checks if a wide character is alphanumeric (function)

ASCII values			characters	iscntrl iswcntrl	isprint iswprint	isspace iswspace	isblank iswblank	isgraph iswgraph	ispunct iswpunct	isalnum iswalnum	isalpha iswalpha	isupper iswupper	islower iswlower	isdigit iswdigit	isxdigit iswxdigit
decimal	hexadecimal	octal
08	\x0\x8	\0\10	control codes (NUL, etc.)	0	0	0	0	0	0	0	0	0	0	0	0
9	\x9	\11	tab (\t)	0	0	0	0	0	0	0	0	0	0	0	0
1013	\xA\xD	\12\15	whitespaces (\n, \v, \f, \r)	0	0	0	0	0	0	0	0	0	0	0	0
1431	\xE\x1F	\16\37	control codes	0	0	0	0	0	0	0	0	0	0	0	0
32	\x20	\40	space	0	0	0	0	0	0	0	0	0	0	0	0
3347	\x21\x2F	\41\57	!"#$%&'()*+,-./	0	0	0	0	0	0	0	0	0	0	0	0
4857	\x30\x39	\60\71	0123456789	0	0	0	0	0	0	0	0	0	0	0	0
5864	\x3A\x40	\72\100	:;<=>?@	0	0	0	0	0	0	0	0	0	0	0	0
6570	\x41\x46	\101\106	ABCDEF	0	0	0	0	0	0	0	0	0	0	0	0
7190	\x47\x5A	\107\132	GHIJKLMNOP QRSTUVWXYZ	0	0	0	0	0	0	0	0	0	0	0	0
9196	\x5B\x60	\133\140	[\]^_`	0	0	0	0	0	0	0	0	0	0	0	0
97102	\x61\x66	\141\146	abcdef	0	0	0	0	0	0	0	0	0	0	0	0
103122	\x67\x7A	\147\172	ghijklmnop qrstuvwxyz	0	0	0	0	0	0	0	0	0	0	0	0
123126	\x7B\x7E	\172\176	{|}~	0	0	0	0	0	0	0	0	0	0	0	0
127	\x7F	\177	backspace character (DEL)	0	0	0	0	0	0	0	0	0	0	0	0