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

# isblank(3)

space or tab character test

## NAME

**isblank** – space or tab character test

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

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

*int*\

**isblank**(*int c*);

## DESCRIPTION

The **isblank**() function tests for a space or tab character. For any locale, this includes the following standard characters:

| |
| --- |
| \`\`\\t'' \`\` '' |

In the "C" locale, a successful **isblank**() test is limited to these characters only. The value of the argument must be representable as an *unsigned char* or the value of EOF.

## RETURN VALUES

The **isblank**() function returns zero if the character tests false and returns 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 **iswblank**() function should be used instead.

## SEE ALSO

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

## STANDARDS

The **isblank**() function conforms to ISO/IEC 9899:1999 (“ISO C99”).