linux - [Solved-5 Solutions] Why does printf not flush after the call unless a newline is in the format string ? - ubuntu - red hat - debian - linux server - linux pc

Why does printf not flush after the call unless a newline is in the format string ?

Print to stderr instead using fprintf:

fprintf(stderr, "I will be printed immediately");

Flush stdout whenever you need it to using fflush:

printf("Buffered, will be flushed");
fflush(stdout); // Will now print everything in the stdout buffer

You can also disable buffering on stdout by using setbuf :

setbuf(stdout, NULL);

It's probably like that because of efficiency and because if you have multiple programs writing to a single TTY, this way you don't get characters on a line interlaced. So if program A and B are outputting, you'll usually get:

program A output
program B output
program B output
program A output
program B output

This stinks, but it's better than

proprogrgraam m AB  ououtputputt
prproogrgram amB A  ououtputtput
program B output

To immediately flush call fflush(stdout) or fflush(NULL) - NULL means flush everything.

stdout is buffered, so will only output after a newline is printed.

To get immediate output, either:

You can fprintf to stderr, which is unbuffered, instead. On the other hand you can flush stdout when you want to. Or you can set stdout to unbuffered.