Defined in header <stdlib.h> | ||
---|---|---|
(1) | ||
size_t wcstombs( char *dst, const wchar_t *src, size_t len ); | (until C99) | |
size_t wcstombs( char *restrict dst, const wchar_t *restrict src, size_t len ); | (since C99) | |
errno_t wcstombs_s( size_t *restrict retval, char *restrict dst, rsize_t dstsz, const wchar_t *restrict src, rsize_t len ); | (2) | (since C11) |
1) Converts a sequence of wide characters from the array whose first element is pointed to by
src
to its narrow multibyte representation that begins in the initial shift state. Converted characters are stored in the successive elements of the char array pointed to by dst
. No more than len
bytes are written to the destination array. Each character is converted as if by a call to
wctomb
, except that the wctomb's conversion state is unaffected. The conversion stops if: * The null character
L'\0'
was converted and stored. The bytes stored in this case are the unshift sequence (if necessary) followed by '\0'
, * A
wchar_t
was found that does not correspond to a valid character in the current C locale. * The next multibyte character to be stored would exceed
len
. If
src
and dst
overlap, the behavior is unspecified. 2) Same as (1), except that
* the function returns its result as an out-parameter
retval
* if the conversion stops without writing a null character, the function will store
'\0'
in the next byte in dst
, which may be dst[len]
or dst[dstsz]]
, whichever comes first (meaning up to len+1/dstsz+1 total bytes may be written). In this case, there may be no unshift sequence written before the terminating null. * if
dst
is a null pointer, the number of wide characters that would be produced is stored in *retval
* the function clobbers the destination array from the terminating null and until
dstsz
* If
src
and dst
overlap, the behavior is unspecified. * the following errors are detected at runtime and call the currently installed constraint handler function:
-
-
retval
orsrc
is a null pointer -
dstsz
orlen
is greater thanRSIZE_MAX
(unlessdst
is null) -
dstsz
is not zero (unlessdst
is null) -
len
is greater thandstsz
and the conversion does not encounter null or encoding error in thesrc
array by the timedstsz
is reached (unlessdst
is null)
-
- As all bounds-checked functions,
wcstombs_s
is only guaranteed to be available if__STDC_LIB_EXT1__
is defined by the implementation and if the user defines__STDC_WANT_LIB_EXT1__
to the integer constant1
before includingstdlib.h
.
Notes
In most implementations, wcstombs
updates a global static object of type mbstate_t
as it processes through the string, and cannot be called simultaneously by two threads, wcsrtombs
or wcstombs_s
should be used in such cases.
POSIX specifies a common extension: if dst
is a null pointer, this function returns the number of bytes that would be written to dst
, if converted. Similar behavior is standard for wcsrtombs
and wcstombs_s
.
Parameters
dst | - | pointer to narrow character array where the multibyte character will be stored |
src | - | pointer to the first element of a null-terminated wide string to convert |
len | - | number of bytes available in the array pointed to by dst |
dstsz | - | max number of bytes that will be written (size of the dst array) |
retval | - | pointer to a size_t object where the result will be stored |
Return value
1) On success, returns the number of bytes (including any shift sequences, but excluding the terminating
'\0'
) written to the character array whose first element is pointed to by dst
. On conversion error (if invalid wide character was encountered), returns (size_t)-1
. 2) Returns zero on success (in which case the number of bytes excluding terminating zero that were, or would be written to
dst
, is stored in *retval
), non-zero on error. In case of a runtime constraint violation, stores (size_t)-1
in *retval
(unless retval
is null) and sets dst[0]
to '\0'
(unless dst
is null or dstmax
is zero or greater than RSIZE_MAX
)Example
#include <stdio.h> #include <stdlib.h> #include <locale.h> int main(void) { // 4 wide characters const wchar_t src[] = L"z\u00df\u6c34\U0001f34c"; // they occupy 10 bytes in UTF-8 char dst[11]; setlocale(LC_ALL, "en_US.utf8"); printf("wide-character string: '%ls'\n",src); for (size_t ndx=0; ndx < sizeof src/sizeof src[0]; ++ndx) printf(" src[%2zu] = %#8x\n", ndx, src[ndx]); int rtn_val = wcstombs(dst, src, sizeof dst); printf("rtn_val = %d\n", rtn_val); if (rtn_val > 0) printf("multibyte string: '%s'\n",dst); for (size_t ndx=0; ndx<sizeof dst; ++ndx) printf(" dst[%2zu] = %#2x\n", ndx, (unsigned char)dst[ndx]); }
Output:
wide-character string: 'zß水🍌' src[ 0] = 0x7a src[ 1] = 0xdf src[ 2] = 0x6c34 src[ 3] = 0x1f34c src[ 4] = 0 rtn_val = 10 multibyte string: 'zß水🍌' dst[ 0] = 0x7a dst[ 1] = 0xc3 dst[ 2] = 0x9f dst[ 3] = 0xe6 dst[ 4] = 0xb0 dst[ 5] = 0xb4 dst[ 6] = 0xf0 dst[ 7] = 0x9f dst[ 8] = 0x8d dst[ 9] = 0x8c dst[10] = 0
References
- C11 standard (ISO/IEC 9899:2011):
- 7.22.8.2 The wcstombs function (p: 360)
- K.3.6.5.2 The wcstombs_s function (p: 612-614)
- C99 standard (ISO/IEC 9899:1999):
- 7.20.8.2 The wcstombs function (p: 324)
- C89/C90 standard (ISO/IEC 9899:1990):
- 4.10.8.2 The wcstombs function
See also
(C95)(C11) | converts a wide string to narrow multibyte character string, given state (function) |
(C11) | converts a narrow multibyte character string to wide string (function) |
C++ documentation for wcstombs |
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