c - Write simultaneousely to two streams

Question

Is there a way to to couple two streams (or file descriptors) together so that writing to one stream will also write to the second one? (C, Linux)

Thanks.

Answer 1

Use funopen or fwopen and supply your own write function that writes to multiple FILE*s.

Example:

FILE *files[2] = ...;

FILE *f = fwopen((void *)files, my_writefn);

// ... use f as you like ...

int my_writefn(void *cookie, const char *data, int n) {
  FILE **files = (FILE **)cookie;
  fwrite(data, n, 1, files[0]);
  return fwrite(data, n, 1, files[1]);
}

(Error handling omitted.)

Note that funopen and fwopen are BSD and not in standard Linux. I'm not aware if there's a Linux-compatible equivalent.