echoBack.c

#include <unistd.h>   /* STDIN_FILENO */
#include <locale.h>   /* LC_ALL, setlocale() */
#include <langinfo.h> /* nl_langinfo(), CODESET */
#include <wchar.h>    /* wchar_t, putwchar() */
#include <iconv.h>    /* iconv_t, iconv_open(), iconv(), iconv_close() */
#include <stdlib.h>   /* malloc(), EXIT_SUCCESS */

int main(void) {
  setlocale(LC_ALL, "");                                            // We initialize the locale
  iconv_t converter = iconv_open("WCHAR_T", nl_langinfo(CODESET));  // We initialize a converter
  wchar_t out;                                                      // We allocate memory for one wide char on stack
  char* pOut = (char*)&out;                                         // We allocate memory for one wide char on stack
  size_t outLeft = sizeof(wchar_t); 

  while(outLeft > 0) {                                              // Until we've read one wide char...
    char in;                                                        // We allocate memory for one byte on stack
    char* pIn=&in;
    size_t inLeft = 1;

    if(read(STDIN_FILENO, pIn, 1) == 0) break;                      // We read one byte from stdin to the buffer
    iconv(converter, &pIn, &inLeft, &pOut, &outLeft);               // We feed the byte to the converter
  }

  iconv_close(converter);                                           // We deinitialize a converter
  wprintf(L"%c\n", out);                                            // We echo the wide char back to stdout
  return EXIT_SUCCESS;
}