c中容易忽视stdout与stderr的细节

int main(int argc, char *argv[])
{
 fprintf(stdout, "normal\n");
 fprintf(stderr, "bad\n");
 return 0;
}

"The stream stderr is unbuffered. The stream stdout is line-buffered when it points to a
     terminal. Partial lines will not appear until fflush(3) or exit(3) is called, or a newline
     is printed. This can produce unexpected results, especially with debugging output.  The
     buffering mode of the standard streams (or any other stream) can be changed using the
     setbuf(3) or setvbuf(3) call. "

int main(int argc, char *argv[])
{
 fprintf(stdout, " normal\n");
 fflush(stdout);
 fprintf(stderr, " bad\n");
 return 0;
}

int main(int argc, char *argv[])
{
 write(1, "normal\n", strlen("normal\n"));
 write(2, "bad\n", strlen("bad\n"));
 return 0;
}

"Note that mixing use of FILEs and raw file descriptors can produce unexpected results and
     should generally be avoided.  A general rule is that file
     descriptors are handled in the kernel, while stdio is just a library. This means for exam-
     ple, that after an exec(), the child inherits all open file descriptors, but all old
     streams have become inaccessible."