---
name: "isblank_l"
section: "3"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/isblank"
---

# isblank\_l(3)

space or tab character test

Part of [isblank(3)](/isblank/3.md).

## NAME

**isblank**, **isblank\_l** – space or tab character test

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

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

*int*\

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

*int*\

**isblank\_l**(*int c*, *locale\_t loc*);

## DESCRIPTION

The **isblank**() and **isblank\_l**() functions test for a space or tab character. For any locale, this includes the following standard characters:

| | |
| --- | --- |
| “\\t” | “ ” |

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

The **isblank\_l**() function takes an explicit locale argument, whereas the **isblank**() function uses the current global or per-thread locale.

## RETURN VALUES

The **isblank**() and **isblank\_l**() 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 **iswblank**() or **iswblank\_l**() function should be used instead.

## SEE ALSO

[ctype(3)](/ctype/3.md), [ctype\_l(3)](/ctype_l/3.md), [iswblank(3)](/iswblank/3.md), [iswblank\_l(3)](/iswblank_l/3.md), [xlocale(3)](/xlocale/3.md), [ascii(7)](/ascii/7.md)

## STANDARDS

The **isblank**() function conforms to ISO/IEC 9899:1999 (“ISO C99”). The **isblank\_l**() function conforms to IEEE Std 1003.1-2008 (“POSIX.1”).