std:: mbrlen

Determines the size, in bytes, of the remainder of the multibyte character whose first byte is pointed to by s , given the current conversion state ps .

This function is equivalent to the call std:: mbrtowc ( nullptr, s, n, ps ? ps : & internal ) for some hidden object internal of type std::mbstate_t , except that the expression ps is evaluated only once.

Parameters

Return value

• ​ 0 ​ if the next n or fewer bytes complete the null character.
• The number of bytes (between 1 and n ) that complete a valid multibyte character.
• std:: size_t ( - 1 ) if encoding error occurs.
• std:: size_t ( - 2 ) if the next n bytes are part of a possibly valid multibyte character, which is still incomplete after examining all n bytes.

Example

#include <clocale>
#include <cwchar>
#include <iostream>
#include <string>
 
int main()
{
    // allow mbrlen() to work with UTF-8 multibyte encoding
    std::setlocale(LC_ALL, "en_US.utf8");
 
    // UTF-8 narrow multibyte encoding
    std::string str = "水"; // or u8"\u6c34" or "\xe6\xb0\xb4"
    std::mbstate_t mb = std::mbstate_t();
 
    // simple use: length of a complete multibyte character
    const std::size_t len = std::mbrlen(&str[0], str.size(), &mb);
    std::cout << "The length of " << str << " is " << len << " bytes\n";
 
    // advanced use: restarting in the middle of a multibyte character
    const std::size_t len1 = std::mbrlen(&str[0], 1, &mb);
    if (len1 == std::size_t(-2))
        std::cout << "The first 1 byte of " << str
                  << " is an incomplete multibyte char (mbrlen returns -2)\n";
 
    const std::size_t len2 = std::mbrlen(&str[1], str.size() - 1, &mb);
    std::cout << "The remaining " << str.size() - 1 << " bytes of " << str
              << " hold " << len2 << " bytes of the multibyte character\n";
 
    // error case:
    std::cout << "Attempting to call mbrlen() in the middle of " << str
              << " while in initial shift state returns "
              << (int)mbrlen(&str[1], str.size(), &mb) << '\n';
}

The length of 水 is 3 bytes.
The first 1 byte of 水 is an incomplete multibyte char (mbrlen returns -2)
The remaining 2 bytes of 水 hold 2 bytes of the multibyte character
Attempting to call mbrlen() in the middle of 水 while in initial shift state returns -1

See also