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

# mblen(3)

get number of bytes in a character

## NAME

**mblen**, **mblen\_l** – get number of bytes in a character

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

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

*int*\

**mblen**(*const char \*s*, *size\_t n*);

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

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

*int*\

**mblen\_l**(*const char \*s*, *size\_t n*, *locale\_t loc*);

## DESCRIPTION

The **mblen**() function computes the length, in bytes, of a multibyte character *s*, according to the current conversion state. Up to *n* bytes are examined.

A call with a null *s* pointer returns nonzero if the current locale requires shift states, zero otherwise. If shift states are required, the shift state is reset to the initial state.

Although the **mblen**() function uses the current locale, the **mblen\_l**() function may be passed a locale directly. See [xlocale(3)](/xlocale/3.md) for more information.

## RETURN VALUES

If *s* is NULL, the **mblen**() function returns nonzero if shift states are supported, zero otherwise.

Otherwise, if *s* is not a null pointer, **mblen**() either returns 0 if *s* represents the null wide character, or returns the number of bytes processed in *s*, or returns -1 if no multibyte character could be recognized or converted. In this case, **mblen**(*Ns*, *'s*) internal conversion state is undefined.

## ERRORS

The **mblen**() function will fail if:

- \[EILSEQ\]

  An invalid multibyte sequence was detected.

- \[EINVAL\]

  The internal conversion state is not valid.

## SEE ALSO

[mbrlen(3)](/mbrlen/3.md), [mbtowc(3)](/mbtowc/3.md), [multibyte(3)](/multibyte/3.md), [xlocale(3)](/xlocale/3.md)

## STANDARDS

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