gistfile1.c

#include <wchar.h>

int main()
{
  mbstate_t mbstate;
  wchar_t const wcs[] = "\U00000055\U0000006E\U00000069\U00000063\U0000006F\U00000064\U00000065";
  wchar_t const* wcsptr = wcs;
  char mbs[256];
  
  memset(&mbstate, 0, sizeof mbstate);
  wcsrtombs(mbs, &wcsptr, sizeof(wcs) / sizeof(wcs[0]), &mbstate);
  printf("%s\n", mbs);
  wprintf("%s\n", wcs);

  return 0;
}