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

# mblen(3)

get number of bytes in a character

## NAME

**mblen** – get number of bytes in a character

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

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

*int*\

**mblen**(*const char \*mbchar*, *size\_t nbytes*);

## DESCRIPTION

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

A call with a null *mbchar* 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.

## RETURN VALUES

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

Otherwise, if *mbchar* is not a null pointer, **mblen**() either returns 0 if *mbchar* represents the null wide character, or returns the number of bytes processed in *mbchar*, 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)

## STANDARDS

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