Question regarding fwrite() and fflush()

[Lew Pitcher]

In a recent reply here, I posted some code that used fwrite() to write
binary data to a file. One version of this code used mmap() to access
this binary data in-situ, and I wonder if I should have called fflush()
before calling mmap().

I understand the where to use fflush() on standard text formatted output
(where you use fprintf(), etc to externalize the output), but I don't see
anything my copies of either the ISO C or POSIX standards that say that
I /should/ use fflush(), but neither do I see anything that says I /need
not/ use fflush().

So, wiser and more experienced minds, should I use fflush() in this case
or not?

[Tim Rentsch]

Post by Lew Pitcher
In a recent reply here, I posted some code that used fwrite() to write
binary data to a file. One version of this code used mmap() to access
this binary data in-situ, and I wonder if I should have called fflush()
before calling mmap().
I understand the where to use fflush() on standard text formatted output
(where you use fprintf(), etc to externalize the output), but I don't see
anything my copies of either the ISO C or POSIX standards that say that
I /should/ use fflush(), but neither do I see anything that says I /need
not/ use fflush().
So, wiser and more experienced minds, should I use fflush() in this case
or not?

Yes, do use fflush().

In the alternative, do a setbuf( file, 0 ) so that 'file' is
unbuffered.

[Lew Pitcher]

Post by Tim Rentsch

Post by Lew Pitcher
In a recent reply here, I posted some code that used fwrite() to write
binary data to a file. One version of this code used mmap() to access
this binary data in-situ, and I wonder if I should have called fflush()
before calling mmap().
I understand the where to use fflush() on standard text formatted output
(where you use fprintf(), etc to externalize the output), but I don't see
anything my copies of either the ISO C or POSIX standards that say that
I /should/ use fflush(), but neither do I see anything that says I /need
not/ use fflush().
So, wiser and more experienced minds, should I use fflush() in this case
or not?

Yes, do use fflush().

As I suspected.
Now, my code includes an fflush() after all the fwrite()s are complete.

Post by Tim Rentsch
In the alternative, do a setbuf( file, 0 ) so that 'file' is
unbuffered.

Thanks

[Lawrence D'Oliveiro]

Post by Lew Pitcher
In a recent reply here, I posted some code that used fwrite() to write
binary data to a file. One version of this code used mmap() to access
this binary data in-situ, and I wonder if I should have called fflush()
before calling mmap().

Yes.

Whether the data is buffered or not, is independent of whether the data is
text or not.