std::wctomb

C++

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Named requirements

Language support library

Concepts library (C++20)

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Technical Specifications

Strings library

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Byte strings

Multibyte strings

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Classes

basic_string

basic_string_view (C++17)

char_traits

Null-terminated multibyte strings

Wide/multibyte conversions
mbsinit
mbtowc mbstowcs btowc mbrtowc mbsrtowcs mbrtoc16 (C++11) mbrtoc32 (C++11) mblen	wctomb wcstombs wctob wcrtomb wcsrtombs c16rtomb (C++11) c32rtomb (C++11) mbrlen
Types
mbstate_t

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.

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

void print_wide(const std::wstring& wstr)
{
    bool shifts = std::wctomb(nullptr, 0); // reset the conversion state
    std::cout << "shift sequences " << (shifts ? "are" : "not" ) << " used\n";
    for (wchar_t wc : wstr) {
        std::string mb(MB_CUR_MAX, '\0');
        int ret = std::wctomb(&mb[0], wc);
        std::cout << "multibyte char " << mb << " is " << ret << " bytes\n";
    }
}

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

Output:

shift sequences not used
multibyte char z is 1 bytes
multibyte char  is 2 bytes
multibyte char  is 3 bytes
multibyte char  is 4 bytes

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 [virtual]	converts a string from internT to externT, such as when writing to file (virtual protected member function of std::codecvt)