##### cppreference.com

##### Search

Create account

##### Namespaces

- Page
- Discussion

##### Variants

##### Views

- View
- Edit
- History

##### Actions

# isalnum

From cppreference.com
< c‎ | string‎ | byte

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.

### [edit] Parameters

ch | - | character to classify

### [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).

Run this code

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

- 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

iswalnum (C95) | checks if a wide character is alphanumeric (function) [edit]
C++ documentation for isalnum

ASCII values (hex) | 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`
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
0 - 8 | `0x00-0x08` | control codes (`NUL`, etc.) | `≠0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0`
9 | `0x09` | tab (`\t`) | `≠0` | `0` | `≠0` | `≠0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0`
10 - 13 | `0x0A-0x0D` | whitespaces (`\n`,`\v`,`\f`,`\r`) | `≠0` | `0` | `≠0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0`
14 - 31 | `0x0E-0x1F` | control codes | `≠0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0`
32 | `0x20` | space | `0` | `≠0` | `≠0` | `≠0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0`
33 - 47 | `0x21-0x2F` | `!"#$%&'()*+,-./` | `0` | `≠0` | `0` | `0` | `≠0` | `≠0` | `0` | `0` | `0` | `0` | `0` | `0`
48 - 57 | `0x30-0x39` | `0123456789` | `0` | `≠0` | `0` | `0` | `≠0` | `0` | `≠0` | `0` | `0` | `0` | `≠0` | `≠0`
58 - 64 | `0x3a-0x40` | `:;<=>?@` | `0` | `≠0` | `0` | `0` | `≠0` | `≠0` | `0` | `0` | `0` | `0` | `0` | `0`
65 - 70 | `0x41-0x46` | `ABCDEF` | `0` | `≠0` | `0` | `0` | `≠0` | `0` | `≠0` | `≠0` | `≠0` | `0` | `0` | `≠0`
71 - 90 | `0x47-0x5A` | `GHIJKLMNOPQRSTUVWXYZ` | `0` | `≠0` | `0` | `0` | `≠0` | `0` | `≠0` | `≠0` | `≠0` | `0` | `0` | `0`
91 - 96 | `0x5B-0x60` | `[\]^_`` | `0` | `≠0` | `0` | `0` | `≠0` | `≠0` | `0` | `0` | `0` | `0` | `0` | `0`
97 -102 | `0x61-0x66` | `abcdef` | `0` | `≠0` | `0` | `0` | `≠0` | `0` | `≠0` | `≠0` | `0` | `≠0` | `0` | `≠0`
103-122 | `0x67-0x7A` | `ghijklmnopqrstuvwxyz` | `0` | `≠0` | `0` | `0` | `≠0` | `0` | `≠0` | `≠0` | `0` | `≠0` | `0` | `0`
123-126 | `0x7B-0x7E` | `{|}~` | `0` | `≠0` | `0` | `0` | `≠0` | `≠0` | `0` | `0` | `0` | `0` | `0` | `0`
127 | `0x7F` | backspace character (`DEL`) | `≠0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0`

Retrieved from "http://en.cppreference.com/mwiki/index.php?title=c/string/byte/isalnum&oldid=83501"