practices/myiconv.c

/* This scratch-program is to show how a possible computation of the output buffer left bytes to 
 * the iconv function parameter fits in a context where the input is obtained
 * from other C Library functions. */
#include <iconv.h>
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char **argv) {
  iconv_t cd = iconv_open("UTF-16", "UTF-8");
  FILE *myutf8= fopen("myutf8.txt", "rb");  // actual decoding is performed beside the input stream, of which FILE be ratherly treated as bynary, according to what GNU C Library recomends with regard to portability, for which the "b" in "rb" stands. (rarely meaningful, yet docummented in fopen's manpage)
  char buf[1000];
  size_t bytes = fread(buf, 1, 1000, myutf8);
  size_t left = 2+bytes*2;  // edge case every utf8_char is one-byte lengthed, and 2-bytes for a initial UTF-16 mark
  char *obuf = malloc(left), *inbuf = buf, *outbuf = obuf;
  size_t conv = iconv(cd, &inbuf, &bytes, &outbuf, &left);
  FILE *myutf16 = fopen("myutf16.txt", "wb");
  fwrite(obuf, 1, outbuf-obuf, myutf16);
  fclose(myutf16);
  fclose(myutf8);
  iconv_close(cd);
  exit(EXIT_SUCCESS);
  return 0;
}