---
name: "isdigit"
section: "3"
platform: "macos"
package: "Libc"
version: "1752.120.2"
release: "macOS 26.5"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/isdigit"
---

# isdigit(3)

decimal-digit character test

## NAME

**isdigit,** **isnumber** – decimal-digit character test

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

**#include \<ctype.h\>**

*int*\

**isdigit**(*int c*);

*int*\

**isnumber**(*int c*);

## DESCRIPTION

The **isdigit**() function tests for a decimal digit character. Regardless of locale, this includes the following characters only:

| |
| --- |
| \`\`0'' \`\`1'' \`\`2'' \`\`3'' \`\`4'' |
| \`\`5'' \`\`6'' \`\`7'' \`\`8'' \`\`9'' |

The **isnumber**() function behaves similarly to **isdigit**(), but may recognize additional characters, depending on the current locale setting.

The value of the argument must be representable as an *unsigned char* or the value of EOF.

## RETURN VALUES

The **isdigit**() and **isnumber**() functions return zero if the character tests false and return non-zero if the character tests true.

## COMPATIBILITY

The 4.4BSD extension of accepting arguments outside of the range of the *unsigned char* type in locales with large character sets is considered obsolete and may not be supported in future releases. The **iswdigit**() function should be used instead.

## SEE ALSO

[ctype(3)](/ctype/3.md), [isalnum\_l(3)](/isalnum_l/3.md), [iswdigit(3)](/iswdigit/3.md), [multibyte(3)](/multibyte/3.md), [ascii(7)](/ascii/7.md)

## STANDARDS

The **isdigit**() function conforms to ISO/IEC 9899:1990 (“ISO C90”).

## HISTORY

The **isnumber**() function appeared in 4.4BSD.