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From: "malaperle at gmail dot com" <sourceware-bugzilla@sourceware.org>
To: gdb-prs@sourceware.org
Subject: [Bug breakpoints/18275] New: dprintf (call style) could
 automatically flush the standard output
Date: Fri, 17 Apr 2015 18:29:00 -0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=18275

            Bug ID: 18275
           Summary: dprintf (call style) could automatically flush the
                    standard output
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: breakpoints
          Assignee: unassigned at sourceware dot org
          Reporter: malaperle at gmail dot com

Created attachment 8251
  --> https://sourceware.org/bugzilla/attachment.cgi?id=8251&action=edit
Sample source file

I am attaching to a program that appears to have output buffering on (setvbuf).
If I use dprintf (call style) to add some debug print-outs, I do not see them
until I call fflush. To improve the out-of-the-box experience, I think dprintf
should flush the stdout. I am not sure whether or not there should be an option
to control this but by default I think it should flush.

Here's an example to illustrate the problem

testDprintf.c:
#include <unistd.h>
#include <stdio.h>

int main() {
    setvbuf(stdout, NULL, _IOFBF, BUFSIZ);
    while (1) {
        sleep(5);
    }
    return 0;
}


gdb ./testDprintf
set dprintf-style call
dprintf testDprintf.c:7, "hello printf\n"
r

Wait a few seconds. You won't see output (unless you wait for a really long
time!). If you interrupt (Ctrl-C) then do a: call fflush(0)
Then you see the printfs appear.

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