Q: My program prompts the user to enter data from the keyboard, then
reads its response. When compiled with a 16-bit compiler like BCC or MSC
it works as expected, but with gcc the prompt doesn't show, or is printed
much later in the program.
Q: My program prints text in a loop, but the text appears on the
screen only after the loop is finished....
Q: Help! I cannot make `gotoxy' work! The text I print appears on
the screen in incorrect locations after I use `gotoxy'!
Q: Why does the text appear in the default colors even though I call
`textcolor' and `textbackground'?
A: Do you write to screen using buffered I/O (fprintf,
fputs and the like) functions, or send your output to the C++
cout stream? Then what you see is the effect of the buffering of
the standard output streams. The buffer is not written to screen until
it's full, or until a newline is output, which might produce very
unpleasant and unexpected behavior when used in interactive programs.
DJGPP library functions use more aggressive buffering than 16-bit real-mode compilers, because delivering the output to the screen requires an expensive switch from protected to real mode and back. DJGPP tries to minimize the amount of these mode switches for performance reasons.
It is usually a bad idea to use buffered I/O in interactive programs; you
should instead use screen-oriented functions like cprintf and
cputs. If you must use buffered I/O, you should be sure that
both stdout and stderr are line-buffered or unbuffered (you
can change the buffering by calling the setvbuf library
function); another solution would be to fflush the output stream
before calling any input function, which will ensure all pending output is
written to the operating system. While this will generally work under
DOS and DJGPP, note that in some cases the operating system might
further buffer your output, so sometimes a call like fsync would
be needed to actually cause the output be delivered to the screen.
The functions that set text attributes only affect the screen-oriented
output (a.k.a. conio) functions (cputs, cprintf etc.),
the text written by fprintf and other stdio functions
doesn't change. This is unlike some 16-bit DOS compilers where
stdio functions can also print colored text.