Error Messages from RTL_FM

fprintf(stderr, "Signal caught, exiting!\n");
fprintf(stderr, "Failed to open rtlsdr device #%d.\n", dongle.dev_index);
fprintf(stderr, "Failed to open %s\n", output.filename);
fprintf(stderr, "\nUser cancel, exiting...\n");
fprintf(stderr, "\nLibrary error %d, exiting...\n", r);