Re: Stream buffering and flushing behaviour

[Marc-Andrà Lureau <marcandre dot lureau at gmail dot com>]

Hi Carlos

On Tue, Jul 7, 2015 at 8:23 PM, Carlos O'Donell <carlos@redhat.com> wrote:
>> with READ_SIZE >= 4096, there is no implicit flush taking place, while
>> with READ_SIZE < 4096 (13 for ex), it does flush to disk and
>> subsequent read after seek will return the expected buffer.
>
> Do you mean `fread after fseek`?

yes

> I don't see anything. Do you have a test case that shows the problem?
> Expected and observed results?

Sorry, the example code is a bit borked, here is a simpler version:

#include <stdio.h>
#include <assert.h>

int main()
{
    FILE *f;
    char foo[4096];
    int n;

    f = fopen("/tmp/test", "w+");
    assert(f);
    fwrite("Hello World!\n", 1, 13, f);

    n = fread(foo, 1, FIRST_READ_SIZE, f);
    assert(n == 0);

    fseek(f, 0, SEEK_SET);
    n = fread(foo, 1, sizeof(foo), f);
    assert(n == 13);
    return 0;
}

Compiled with -DFIRST_READ_SIZE=4096 = fail, -DFIRST_READ_SIZE=13 = pass.

Is this expected?

thanks