NAME
mbrtowc() — convert a character to a wide-character code (restartable)
SYNOPSIS
#include <wchar.h>
size_t mbrtowc(wchar_t *__restrict pwc, const char *__restrict s, size_t n, mbstate_t *__restrict ps);
DESCRIPTION
If
s
is a null pointer, the
mbrtowc()
function is equivalent to the call:
In this case, the values of the arguments
pwc
and
n
are ignored.
If
s
is not a null pointer, the
mbrtowc()
function inspects at most
n
bytes beginning at the byte pointed to by
s
to determine the number of bytes needed to complete the next character
(including any shift sequences).
If the function determines that the next character is completed,
it determines the value of the corresponding wide-character and then, if
pwc
is not a null pointer, stores that value in the object pointed to by
pwc.
If the corresponding wide-character is the null wide-character,
the resulting state described is the initial conversion state.
If
ps
is a null pointer, the
mbrtowc()
function uses its own internal mbstate_t object, which is initialized
at program startup to the initial conversion state.
Otherwise, the mbstate_t object pointed to by
ps
is used to completely describe the current conversion state of
the associated character sequence.
APPLICATION USAGE
The prototype of this function is available to applications
if they are:
- a.
c99
conformant.
- b.
Compiled with
-D_XOPEN_SOURCE
macro with a value >=500.
- c.
Compiled with
-D_POSIX_C_SOURCE
macro with a value >= 200112.
EXTERNAL INFLUENCES
Environment Variables
The behavior of this function is affected by the
LC_CTYPE
category of the current locale.
RETURN VALUE
The
mbrtowc()
function returns the first of the following that applies:
- 0
If the next
n
or fewer bytes complete the character that corresponds to
the null wide-character (which is the value stored).
- Positive
If the next
n
or fewer bytes complete a valid character (which is the value stored);
the value returned is the number of bytes that complete the character.
- (size_t)-2
If the next
n
bytes contribute to an incomplete but potentially valid character, and all
n
bytes have been processed (no value is stored). 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).
- (size_t)-1
If an encoding error occurs, in which case the next
n
or fewer bytes do not contribute to a complete and valid character
(no value is stored). In this case,
EILSEQ
is stored in
errno
and the conversion state is undefined.
ERRORS
The
mbrtowc()
function may fail if:
- EILSEQ
Invalid character sequence is detected.
- EINVAL
ps
points to an object that contains an invalid conversion state.
WARNINGS
With the exception of ASCII
characters, the code values of wide characters (type of
wchar_t)
are specific to the effective locale specified by the
LC_CTYPE
environment variable.
These values may not be compatible with values obtained
by specifying other locales that are supported now,
or which may be supported in the future.
It is recommended that wide character constants
and wide string literals (see the
C Reference Manual)
not be used, and that wide character code values not be stored
in files or devices because future standards may dictate changes
in the code value assignments of the wide characters.
However, wide character constants and wide string literals
corresponding to the characters of the ASCII
code set can be safely used since their values are guaranteed
to be the same as their ASCII code set values.
AUTHOR
mbrtowc()
was developed by HP and Mitsubishi Electric Corporation.
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