printf("hello");

[BigZero]

hello ppl,

can any body help how printf(""); internal works, i had one
problem with printf, is printf ay thing to do with memory allocation
or something to do with malloc() function.

Thanks
VM

[Bill Marcum]

You can read the source code of libc6, but perhaps you could say what
your problem with printf was. Maybe it had something to do with locale?

[BigZero]

but perhaps you could say what
> your problem with printf was. Maybe it had something to do with locale?

ok here is the problem...ok i have the 32 bit grep-2.5 code and i m
porting that into 64 bit.her the small problem when allocate memory

[code]
/* Allocate N bytes of memory dynamically, with error checking. */

void *
xmalloc (size_t n)
{
void *p;
printf("Magic");
p = malloc (n);
if (p == 0)
xalloc_die ();
return p;
}
[/code]

will this code work fine allocates memory and grep works fine and you
get the result too, here the code that has the problem.

[code]
/* Allocate N bytes of memory dynamically, with error checking. */

void *
xmalloc (size_t n)
{
void *p;
p = malloc (n);
if (p == 0)
xalloc_die ();
return p;
}
[/code]

when you remove the printf() it allocates or gives array out of bound
exception as we known as a "segmentation fault".
so i wanted to known what actual the printf is doing here.

thanks
VM

[Nathan Seese]

I think they show a /possible/ implementation of printf() in k&r, which
you really need anyway if you're writing C.

--
The preceding message is brought to you by Water(TM)

[BigZero]

> you really need anyway if you're writing C.

well i told you that i m porting any 32 bit application to 64bit
application.....

Thanks
VM

[Robert Riches]

The personality() system call may end up being your friend.
It was mine when I got the 32-bit-only-and-proud-of-it
Squeak Smalltalk implementation working on my 64-bit DEC
Alpha a few years ago.

--
Robert Riches
spamt...@verizon.net
(Yes, that is one of my email addresses.)

[BigZero]

> The personality() system call may end up being your friend.
> It was mine when I got the 32-bit-only-and-proud-of-it

well thanks for that, but what is it?

[Ray]

yes, printf will CAN internal malloc (i can't remember ever seeing
this specified in the manpages on any of the unices i have worked
on).. if you want to be sure that there is no allocations you should
use sprintf

struct iov iv;
char buf[1000];
iv.iov_base = buf;
iv.iov_len = snprintf(buf, 1000, "....");
writev(STDIO_FILENO, &iv, 1);

this is very simplified code (no err check etc) but with the local
stack buffer being used you can ensure that your write to stdout wont
alloc any memory -- i may be wrong about the sys call write(2) but i
belive it do NOT guarantee that there is no copy of the buf passed to
it and i believe that the scatter writev will use ensure that there is
no buffer copy at the system level.

however, if you are experiencing problem with printf() i would suggest
that it might be an application problem rather than a printf() problem

[Ray]

On 2 Sep, 12:05, Bill Marcum <marcumb...@bellsouth.net> wrote:

oh yes, and if you care enough about checking the printf()'s
potentially allocation you should use strace to see what system calls
are being hit at the time your printf happens -- watch out for brk()
system calls which will be the system providing memory back to the
processes (more specifically extending the virt address space of the
process)

[Robert Riches]

Do you not have access to man pages or a search engine?
Unless you're paying me to spoon feed you, you need to be
doing a little bit of the work yourself. Please try the
following two commands:

man man
man personality

Putting the following into Google's search term field should
find useful hits:

linux personality "system call"

The personality() system call changes some things about how
the kernel interacts with the application. In my case, when
I worked on getting 32-bit-only Squeak (free Smalltalk)
working on a DEC Alpha, I added a call to personality() at
the very beginning of main() to tell the kernel to act like
a 32-bit Linux environment, so malloc() would return memory
in the lower 2-4GB of the address space. Then, when Squeak
stuffed a pointer into an 'int' variable and then later took
it back out and put it back into a pointer variable and then
used the pointer, everything worked as the program had
intended. (In the case of the DEC Alpha, I had to also use
the -taso or '-w taso' compilation option. I also had to
hack Squeak's configuration script to recognize Alpha as
little endian rather than big endian.)

HTH

[BigZero]

Thanks, now i belive it time to learn, more then what i think.....

Thanks
VM