NAME¶

std::mbrtowc - std::mbrtowc

Synopsis¶

Defined in header <cwchar>
std::size_t mbrtowc( wchar_t* pwc,

const char* s,
std::size_t n,

std::mbstate_t* ps );

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.

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

Return value¶

The first of the following that applies:

* 0 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.

Example¶

// Run this code

#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"zß水𝄋"
// 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 ß
Next 3 bytes are the character 水
Next 4 bytes are the character 𝄋

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_in converts a string from ExternT to InternT, such as when reading from file
[virtual] (virtual protected member function of
std::codecvt<InternT,ExternT,StateT>)
C documentation for
mbrtowc