mbrtoc16() in C/C++ with Examples

The mbrtoc16() is a built-in function in C/C++ which converts a narrow multibyte character to a 16 bit character representation. It is defined within the uchar.h header file of C++.

Syntax:

ssize_t mbrtoc16( char16_t* pc16, const char* s, size_t n, mbstate_t* ps);

Parameters: The function accepts four mandatory parameter which are described below:

• s : specifies to the multibyte character to convert.
• pc16 : specifies to the memory location to store the resulting 16 bit character.
• n : specifies the maximum number of bytes in s to convert.
• ps : specifies to an mbstate_t object used when interpreting the multibyte string.

Return Value: The function returns five values as follows:

• 0 if the converted character is a null character.
• the number of bytes (at most n) of the multibyte character that was successfully converted to 16 bit character.
• -3 if the next char16_t from a multi-char16_t character (e.g. a surrogate pair) has now been written to *pc16. No bytes are processed from the input in this case.
• -2 if the next n bytes constitute an incomplete, but so far valid, multibyte character. In this case nothing is written to *pc16.
• -1 if encoding error occurs. In this case nothing is written to *pc16, errno is set to EILSEQ and the value of *ps is unspecified.

Below programs illustrate the above function.

Program 1:

// C++ program to illustrate the
// mbrtoc16() function
#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <uchar.h>
#include <wchar.h>
using namespace std;

int main(void)
{
    char16_t pc16;
    char s[] = "G";
    mbstate_t ps{};
    int length;

    // initializing the function
    length = mbrtoc16(&pc16, s, MB_CUR_MAX, &ps);

    if (length < 0) {
        perror("mbrtoc16() fails to convert");
        exit(-1);
    }

    cout << "Multibyte string = " << s << endl;
    cout << "Length = " << length << endl;
    printf("16-bit character = 0g%02hd\n", pc16);
}

Output:

Multibyte string = G
Length = 1
16-bit character = 0g71

Program 2:

// C++ program to illustrate the
// mbrtoc16() function
#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <uchar.h>
#include <wchar.h>
using namespace std;

int main(void)
{
    char16_t pc16;
    char s[] = "";
    mbstate_t ps{};
    int length;
    // initializing the function
    length = mbrtoc16(&pc16, s, MB_CUR_MAX, &ps);

    if (length < 0) {
        perror("mbrtoc16() fails to convert");
        exit(-1);
    }

    cout << "Multibyte string = " << s << endl;
    cout << "Length = " << length << endl;
    printf("16-bit character = 1e%04xy\n", pc16);
}

Output:

Multibyte string = 
Length = 0
16-bit character = 1e0000y