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


mblen - get number of bytes in a character


#include <stdlib.h>

int mblen(const char *
s, size_t n);


[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, mblen() shall determine the number of bytes constituting the character pointed to by s. Except that the shift state of mbtowc() is not affected, it shall be equivalent to:

mbtowc((wchar_t *)0, s, n);

The implementation shall behave as if no function defined in this volume of POSIX.1-2008 calls mblen().

The behavior of this function is affected by the LC_CTYPE category of the current locale. For a state-dependent encoding, this function shall be placed into its initial state by a call for which its character pointer argument, s, is a null pointer. Subsequent calls with s as other than a null pointer shall cause the internal state of the function to be altered as necessary. A call with s as a null pointer shall cause this function to return a non-zero value if encodings have state dependency, and 0 otherwise. If the implementation employs special bytes to change the shift state, these bytes shall not produce separate wide-character codes, but shall be grouped with an adjacent character. Changing the LC_CTYPE category causes the shift state of this function to be unspecified.

[CX] [Option Start] The mblen() function need not be thread-safe. [Option End]


If s is a null pointer, mblen() shall return a non-zero or 0 value, if character encodings, respectively, do or do not have state-dependent encodings. If s is not a null pointer, mblen() shall either return 0 (if s points to the null byte), or return the number of bytes that constitute the character (if the next n or fewer bytes form a valid character), or return -1 (if they do not form a valid character) [CX] [Option Start]  and may set errno to indicate the error. [Option End] In no case shall the value returned be greater than n or the value of the {MB_CUR_MAX} macro.


The mblen() function may fail if:

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

The following sections are informative.










mbtowc, mbstowcs, wctomb, wcstombs

XBD <stdlib.h>


First released in Issue 4. Aligned with the ISO C standard.

Issue 7

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0367 [109] is applied.

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

End of informative text.


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