mbsinit

#include <locale.h>
#include <string.h>
#include <stdio.h>
#include <wchar.h>
 
int main(void)
{
 // allow mbrlen() to work with UTF-8 multibyte encoding
 setlocale (LC_ALL, "en_US.utf8");
 // UTF-8 narrow multibyte encoding
 const char* str = u8"水"; // or u8"\u6c34" or "\xe6\xb0\xb4"
 static mbstate_t mb; // zero-initialize
 (void)mbrlen (&str[0], 1, &mb);
 if (!mbsinit(&mb)) {
 printf ("After processing the first 1 byte of %s,\n"
 "the conversion state is not initial\n\n", str);
 }
 
 (void)mbrlen (&str[1], strlen (str), &mb);
 if (mbsinit(&mb)) {
 printf ("After processing the remaining 2 bytes of %s,\n"
 "the conversion state is initial conversion state\n", str);
 }
}

After processing the first 1 byte of 水,
the conversion state is not initial
 
After processing the remaining 2 bytes of 水,
the conversion state is initial conversion state