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MBLEN(3) NetBSD Library Functions Manual MBLEN(3)
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mblen -- get number of bytes in a multibyte character
Standard C Library (libc, -lc)
mblen(const char *s, size_t n);
The mblen() function usually determines the number of bytes in a multi-
byte character pointed to by s and returns it. This function shall only
examine max n bytes of the array beginning from s.
In state-dependent encodings, s may point the special sequence bytes to
change the shift-state. Although such sequence bytes corresponds to no
individual wide-character code, the mblen() changes the own state by them
and treats them as if they are a part of the subsequent multibyte charac-
Unlike mbrlen(3), the first n bytes pointed to by s need to form an
entire multibyte character. Otherwise, this function causes an error.
mblen() is equivalent to the following call, except the internal state of
the mbtowc(3) function is not affected:
mbtowc(NULL, s, n);
Calling any other functions in Standard C Library (libc, -lc) never
changes the internal state of mblen(), except for calling setlocale(3)
with the LC_CTYPE category changed to that of the current locale. Such
setlocale(3) calls cause the internal state of this function to be inde-
The behaviour of mblen() is affected by the LC_CTYPE category of the cur-
These are the special cases:
s == NULL mblen() initializes its own internal state to an initial
state, and determines whether the current encoding is state-
dependent. This function returns 0 if the encoding is state-
independent, otherwise non-zero.
n == 0 In this case, the first n bytes of the array pointed to by s
never form a complete character. Thus, mblen() always fails.
Normally, mblen() returns:
0 s points to a nul byte (`\0').
positive The value returned is a number of bytes for the valid multi-
byte character pointed to by s. There are no cases that this
value is greater than n or the value of the MB_CUR_MAX macro.
-1 s points to an invalid or incomplete multibyte character.
The mblen() also sets errno to indicate the error.
When s is equal to NULL, the mblen() returns:
0 The current encoding is state-independent.
non-zero The current encoding is state-dependent.
mblen() may cause an error in the following case:
[EILSEQ] s points to an invalid or incomplete multibyte charac-
mbrlen(3), mbtowc(3), setlocale(3)
The mblen() function conforms to ANSI X3.159-1989 (``ANSI C89'').
NetBSD 7.1.2 February 3, 2002 NetBSD 7.1.2