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Showing content from https://en.cppreference.com/w/cpp/language/../string/multibyte/mbrtowc.html below:

std::mbrtowc - cppreference.com

Converts a narrow multibyte character to a wide character.

If s is not a null pointer, inspects at most n bytes of the multibyte character string, beginning with the byte pointed to by s to determine the number of bytes necessary to complete the next multibyte character (including any shift sequences). If the function determines that the next multibyte character in s is complete and valid, converts it to the corresponding wide character and stores it in *pwc (if pwc is not null).

If s is a null pointer, the values of n and pwc are ignored and call is equivalent to std::mbrtowc(nullptr, "", 1, ps).

If the wide character produced is the null character, the conversion state stored in *ps is the initial shift state.

[edit] Parameters pwc - pointer to the location where the resulting wide character will be written s - pointer to the multibyte character string used as input n - limit on the number of bytes in s that can be examined ps - pointer to the conversion state used when interpreting the multibyte string [edit] Return value

The first of the following that applies:

â0â if the character converted from s (and stored in pwc if non-null) was the null character.
the number of bytes [1...n] of the multibyte character successfully converted from s.
static_cast<std::size_t>(-2) if the next n bytes constitute an incomplete, but so far valid, multibyte character. Nothing is written to *pwc.
static_cast<std::size_t>(-1) if encoding error occurs. Nothing is written to *pwc, the value EILSEQ is stored in errno and the value of *ps is left unspecified.

[edit] Example

#include <clocale>
#include <cstring>
#include <cwchar>
#include <iostream>
 
void print_mb(const char* ptr)
{
    std::mbstate_t state = std::mbstate_t(); // initial state
    const char* end = ptr + std::strlen(ptr);
    int len;
    wchar_t wc;
    while ((len = std::mbrtowc(&wc, ptr, end-ptr, &state)) > 0)
    {
        std::wcout << "Next " << len << " bytes are the character " << wc << '\n';
        ptr += len;
    }
}
 
int main()
{
    std::setlocale(LC_ALL, "en_US.utf8");
    // UTF-8 narrow multibyte encoding
    const char* str = "z\u00df\u6c34\U0001d10b"; // or u8"zÃæ°´ð"
                      // or "\x7a\xc3\x9f\xe6\xb0\xb4\xf0\x9d\x84\x8b";
    print_mb(str);
}

Output:

Next 1 bytes are the character z
Next 2 bytes are the character Ã
Next 3 bytes are the character æ°´
Next 4 bytes are the character ð

[edit] See also converts the next multibyte character to wide character
(function) [edit] converts a wide character to its multibyte representation, given state
(function) [edit] converts a string from ExternT to InternT, such as when reading from file
(virtual protected member function of std::codecvt<InternT,ExternT,StateT>) [edit]

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