The Open Group Base Specifications Issue 7
IEEE Std 1003.1-2008, 2016 Edition
Copyright © 2001-2016 The IEEE and The Open Group


mbrlen - get number of bytes in a character (restartable)


#include <wchar.h>

size_t mbrlen(const char *restrict
s, size_t n,
       mbstate_t *restrict


[CX] [Option Start] The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2008 defers to the ISO C standard. [Option End]

If s is not a null pointer, mbrlen() shall determine the number of bytes constituting the character pointed to by s. It shall be equivalent to:

mbstate_t internal;
mbrtowc(NULL, s, n, ps != NULL ? ps : &internal);

If ps is a null pointer, the mbrlen() function shall use its own internal mbstate_t object, which is initialized at program start-up to the initial conversion state. Otherwise, the mbstate_t object pointed to by ps shall be used to completely describe the current conversion state of the associated character sequence. The implementation shall behave as if no function defined in this volume of POSIX.1-2008 calls mbrlen().

The behavior of this function is affected by the LC_CTYPE category of the current locale.

[CX] [Option Start] The mbrlen() function need not be thread-safe if called with a NULL ps argument. [Option End]

The mbrlen() function shall not change the setting of errno if successful.


The mbrlen() function shall return the first of the following that applies:

If the next n or fewer bytes complete the character that corresponds to the null wide character.
If the next n or fewer bytes complete a valid character; the value returned shall be the number of bytes that complete the character.
If the next n bytes contribute to an incomplete but potentially valid character, and all n bytes have been processed. When n has at least the value of the {MB_CUR_MAX} macro, this case can only occur if s points at a sequence of redundant shift sequences (for implementations with state-dependent encodings).
If an encoding error occurs, in which case the next n or fewer bytes do not contribute to a complete and valid character. In this case, [EILSEQ] shall be stored in errno and the conversion state is undefined.


The mbrlen() function shall fail if:

An invalid character sequence is detected. [CX] [Option Start]  In the POSIX locale an [EILSEQ] error cannot occur since all byte values are valid characters. [Option End]

The mbrlen() function may fail if:

ps points to an object that contains an invalid conversion state.

The following sections are informative.










mbsinit, mbrtowc

XBD <wchar.h>


First released in Issue 5. Included for alignment with ISO/IEC 9899:1990/Amendment 1:1995 (E).

Issue 6

The mbrlen() prototype is updated for alignment with the ISO/IEC 9899:1999 standard.

Issue 7

Austin Group Interpretation 1003.1-2001 #170 is applied.

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0368 [109,105] is applied.

POSIX.1-2008, Technical Corrigendum 2, XSH/TC2-2008/0204 [663,674] is applied.

End of informative text.


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