printf returns the “number of characters transmitted to the output stream or negative value if an output error or an encoding error (for string and character conversion specifiers) occurred”, so it won’t ever return zero for that call (https://en.cppreference.com/w/c/io/fprintf)
I also think this optimally should do something like
int x = printf("Hello world!\n");
if(x<0) return x; // maybe fflush here, too, ignoring errors?
return fflush(stdout);
Logging an error message to stderr should be considered, too. I would ignore any errors from that, but attempting to syslog those or to write them to the console could be a better choice.
