isalnum - cppreference.com (original) (raw)

| | | | | ---------------------- | | | | 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.

[edit] Parameters

[edit] Return value

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

[edit] Example

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

#include <ctype.h> #include <locale.h> #include <stdio.h>   int main(void) { unsigned char c = '\xdf'; // German letter ß 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

[edit] References

• C23 standard (ISO/IEC 9899:2024):

• 7.4.1.1 The isalnum function (p: TBD)

• C17 standard (ISO/IEC 9899:2018):

• 7.4.1.1 The isalnum function (p: 145)

• 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

[edit] See also