#include <stdio.h>
#include <wchar.h>
#include <wctype.h>
#include <locale.h>
#define LEN 5

int main() {
  char readInByte[LEN], writeOutByte[LEN];     // holds the character bytes
  const char *readInByteP[] = {readInByte};    // help pointer
  wchar_t readInWC[LEN], writeOutWC[LEN];      // holds the wide characters
  const wchar_t *writeOutWCP[] = {writeOutWC}; // help pointer
  wctrans_t wctransDesc;                       // holds the descriptor for conversion
  int i, ret;
  const char myLocale[] = "ja_JP.utf8";
  char *localeSet;

  readInByte[0] = 0xc3; readInByte[1] = 0x84;  // german umlaut A (upper) in UTF-8
  readInByte[2] = 0xc3; readInByte[3] = 0xa4;  // german umlaut a (lower) in UTF-8
  readInByte[4] = 0;

  // print out the input
  printf("german umlaut A (upper) UTF-8: %hhx %hhx\n", readInByte[0], readInByte[1]);
  printf("german umlaut a (lower) UTF-8: %hhx %hhx\n", readInByte[2], readInByte[3]);

  if((localeSet = setlocale(LC_CTYPE, myLocale)) == NULL) { perror("setlocale"); exit(1); }
  else printf("locale set: %s\n", localeSet);
  ret = mbsrtowcs(readInWC, readInByteP, LEN, NULL); // convert bytes to wide chars
  printf("number of wide chars: %i\n", ret);
  wctransDesc = wctrans("tolower");            // get descriptor for wc operation
  if(wctransDesc == 0) { perror("wctransDesc"); exit(1); }

  // make the transformation according to descriptor
  i=0; while((writeOutWC[i] = towctrans(readInWC[i], wctransDesc)) != L'\0') i++;
  
  ret = wcsrtombs(writeOutByte, writeOutWCP, LEN, NULL); // convert wide chars to bytes
  printf("number of bytes: %i\n", ret);

  // print out the result
  printf("german umlaut A tolower(): %hhx %hhx\n", writeOutByte[0], writeOutByte[1]);
  printf("german umlaut a tolower(): %hhx %hhx\n", writeOutByte[2], writeOutByte[3]);

  return 0;
}