mbrtoc32() in C/C++ with Examples

The mbrtoc32() is a built-in function in C/C++ which converts a narrow multibyte character to a 32 bit character representation. It is defined within the uchar.h header file of C++.

Syntax:

size_t mbrtoc32( char32_t* pc32, 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.
pc32 : specifies to the memory location to store the resulting 32 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 32 bit character.
-3 if the next char16_t from a multi-char32_t character (e.g. a surrogate pair) has now been written to *pc32. 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 *pc32.
-1 if encoding error occurs. In this case nothing is written to *pc32, 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 
// mbrtoc32() function 
#include <cstdio> 
#include <cstdlib> 
#include <iostream> 
#include <uchar.h> 
#include <wchar.h> 
using namespace std; 
  
int main(void) 
{ 
    char32_t pc32; 
    char s[] = "S"; 
    mbstate_t ps{}; 
    int length; 
  
    // initializing the function 
    length = mbrtoc32(&pc32, s, MB_CUR_MAX, &ps); 
  
    if (length < 0) { 
        perror("mbrtoc32() fails to convert"); 
        exit(-1); 
    } 
  
    cout << "Multibyte string = " << s << endl; 
    cout << "Length = " << length << endl; 
    printf("32-bit character = 0x%04hx\n", pc32); 
    return 0; 
} 

Output:

Multibyte string = S
Length = 1
32-bit character = 0x0053

Program 2:

// C++ program to illustrate the 
// mbrtoc32() function 
#include <cstdio> 
#include <cstdlib> 
#include <iostream> 
#include <uchar.h> 
#include <wchar.h> 
using namespace std; 
  
int main(void) 
{ 
    char32_t pc32; 
    char s[] = "S"; 
    mbstate_t ps{}; 
    int length; 
  
    // initializing the function 
    length = mbrtoc32(&pc32, s, MB_CUR_MAX, &ps); 
  
    if (length < 0) { 
        perror("mbrtoc32() fails to convert"); 
        exit(-1); 
    } 
  
    cout << "Multibyte string = " << s << endl; 
    cout << "Length = " << length << endl; 
    printf("32-bit character = 0x%08hx\n", pc32); 
    return 0; 
} 

Output:

Multibyte string = S
Length = 1
32-bit character = 0x00000053

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