c - Why does my output only print if there is another print after it?

Question

Interesting little bug here:

if (host != NULL) {
    printf("hi");
} else {
    printf("FAIL");
}
return 0;

doesn't print anything at all, but:

if (host != NULL) {
    printf("hi");
} else {
    printf("FAIL");
}   
fprintf(stdout, "
%s
", (char *)&additionalargs);
return 0;

prints

hi

abc

Does anyone know why this is?

Answer 1

printf output to stdout is buffered. You might want to look at fflush