NAME¶

std::wctomb - std::wctomb

Synopsis¶

Defined in header <cstdlib>
int wctomb( char* s, wchar_t wc );

Converts a wide character wc to multibyte encoding and stores it (including any
shift sequences) in the char array whose first element is pointed to by s. No more
than MB_CUR_MAX characters are stored. The conversion is affected by the current
locale's LC_CTYPE category.

If wc is the null character, the null byte is written to s, preceded by any shift
sequences necessary to restore the initial shift state.

If s is a null pointer, resets the global conversion state and determines whether
shift sequences are used.

Parameters¶

s - pointer to the character array for output
wc - wide character to convert

Return value¶

If s is not a null pointer, returns the number of bytes that are contained in the
multibyte representation of wc or -1 if wc is not a valid character.

If s is a null pointer, resets its internal conversion state to represent the
initial shift state and returns 0 if the current multibyte encoding is not
state-dependent (does not use shift sequences) or a non-zero value if the current
multibyte encoding is state-dependent (uses shift sequences).

Notes¶

Each call to wctomb updates the internal global conversion state (a static object of
type std::mbstate_t, only known to this function). If the multibyte encoding uses
shift states, this function is not reentrant. In any case, multiple threads should
not call wctomb without synchronization: std::wcrtomb may be used instead.

Example¶

// Run this code

#include <clocale>
#include <cstdlib>
#include <iomanip>
#include <iostream>
#include <string>

void print_wide(const std::wstring& wstr)
{
bool shifts = std::wctomb(nullptr, 0); // reset the conversion state
std::cout << "shift sequences are " << (shifts ? "" : "not" )
<< " used\n" << std::uppercase << std::setfill('0');
for (const wchar_t wc : wstr)
{
std::string mb(MB_CUR_MAX, '\0');
const int ret = std::wctomb(&mb[0], wc);
const char* s = ret > 1 ? "s" : "";
std::cout << "multibyte char '" << mb << "' is " << ret
<< " byte" << s << ": [" << std::hex;
for (int i{0}; i != ret; ++i)
{
const int c = 0xFF & mb[i];
std::cout << (i ? " " : "") << std::setw(2) << c;
}
std::cout << "]\n" << std::dec;
}
}

int main()
{
std::setlocale(LC_ALL, "en_US.utf8");
// UTF-8 narrow multibyte encoding
std::wstring wstr = L"z\u00df\u6c34\U0001d10b"; // or L"zß水𝄋"
print_wide(wstr);
}

Output:¶

shift sequences are not used
multibyte char 'z' is 1 byte: [7A]
multibyte char 'ß' is 2 bytes: [C3 9F]
multibyte char '水' is 3 bytes: [E6 B0 B4]
multibyte char '𝄋' is 4 bytes: [F0 9D 84 8B]

See also¶

mbtowc converts the next multibyte character to wide character
(function)
wcrtomb converts a wide character to its multibyte representation, given state
(function)
do_out converts a string from InternT to ExternT, such as when writing to file
[virtual] (virtual protected member function of
std::codecvt<InternT,ExternT,StateT>)
C documentation for
wctomb