How to create a process that uses 5Gb of memory?

[P]

I want to write a platform independent program that would use up at
least 5Gb of memory for testing purposes. How would I do that?

Thanks!

P

[Flash Gordon]

P wrote, On 03/08/07 21:56:

I want to write a platform independent program that would use up at
least 5Gb of memory for testing purposes. How would I do that?

It won't be very platform independent since most platforms do not have
5GB of memory and many that might will not allow one process to grab
that much. For those platforms that do then try mallocing a 5GB chunk,
if that fails try mallocing 1GB 5 times. Make sure you also write to the
memory otherwise you might not have what has been reported.

Mind you, I find it hard to see why you need to use up that much memory
for testing purposes.
--
Flash Gordon

[Peter J. Holzer]

On 2007-08-06 08:18, Richard <rg****@gmail.comwrote:

Is a char a byte now? I lose track.

A "byte" in C-speak has been defined as the space occupied by a "char"
at least since C89.
In other contexts, a "byte" may be defined differently (e.g., as
"exactly 8 bits").

hp

--
_ | Peter J. Holzer | I know I'd be respectful of a pirate
|_|_) | Sysadmin WSR | with an emu on his shoulder.
| | | hj*@hjp.at |
__/ | http://www.hjp.at/ | -- Sam in "Freefall"

[Richard]

"Peter J. Holzer" <hj*********@hjp.atwrites:

On 2007-08-06 08:18, Richard <rg****@gmail.comwrote:

>Is a char a byte now? I lose track.

A "byte" in C-speak has been defined as the space occupied by a "char"
at least since C89.
In other contexts, a "byte" may be defined differently (e.g., as
"exactly 8 bits").

So A byte is CHAR_BITS? Which is in 99.999% of the time 8 bits?

[santosh]

Richard wrote:

"Peter J. Holzer" <hj*********@hjp.atwrites:

>On 2007-08-06 08:18, Richard <rg****@gmail.comwrote:

>>Is a char a byte now? I lose track.

A "byte" in C-speak has been defined as the space occupied by a "char"
at least since C89.
In other contexts, a "byte" may be defined differently (e.g., as
"exactly 8 bits").

So A byte is CHAR_BITS?

In C, yes.

Which is in 99.999% of the time 8 bits?

Maybe not quite that much, if you consider the large embedded world, where
the bulk of C programming is currently happenning.

[Richard]

santosh <sa*********@gmail.comwrites:

Richard wrote:

>"Peter J. Holzer" <hj*********@hjp.atwrites:

>>On 2007-08-06 08:18, Richard <rg****@gmail.comwrote:
Is a char a byte now? I lose track.

A "byte" in C-speak has been defined as the space occupied by a "char"
at least since C89.
In other contexts, a "byte" may be defined differently (e.g., as
"exactly 8 bits").

So A byte is CHAR_BITS?

In C, yes.

>Which is in 99.999% of the time 8 bits?

Maybe not quite that much, if you consider the large embedded world, where
the bulk of C programming is currently happenning.

Venturing off topic here, how many of those system is a "byte" not 8
bits?

[Flash Gordon]

Richard wrote, On 06/08/07 11:55:

santosh <sa*********@gmail.comwrites:

>Richard wrote:

>>"Peter J. Holzer" <hj*********@hjp.atwrites:

On 2007-08-06 08:18, Richard <rg****@gmail.comwrote:
Is a char a byte now? I lose track.
A "byte" in C-speak has been defined as the space occupied by a "char"
at least since C89.
In other contexts, a "byte" may be defined differently (e.g., as
"exactly 8 bits").
So A byte is CHAR_BITS?

In C, yes.

>>Which is in 99.999% of the time 8 bits?

Maybe not quite that much, if you consider the large embedded world, where
the bulk of C programming is currently happenning.

Venturing off topic here, how many of those system is a "byte" not 8
bits?

I don't know numbers, but certainly the C compiler for the Texas
Instruments TMS320C1x/2x/3x/4x/5x and I believe a lot of the other DSP
chips from other manufacturers as well.
--
Flash Gordon

[Richard Heathfield]

santosh said:

Richard wrote:

>>
Is a char a byte now? I lose track.

In C a char is always a byte.

Anyone who can go a week (let alone many, many months) in this newsgroup
without learning that a char is defined to be 1 byte wide is either
unable or unwilling to learn.

--
Richard Heathfield <http://www.cpax.org.uk>
Email: -www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

[Richard]

Richard Heathfield <rj*@see.sig.invalidwrites:

santosh said:

>Richard wrote:

>>>
Is a char a byte now? I lose track.

In C a char is always a byte.

Anyone who can go a week (let alone many, many months) in this newsgroup
without learning that a char is defined to be 1 byte wide is either
unable or unwilling to learn.

Is that you being a snide, self absorbed bighead again, or did you have something to
offer the thread?

[Malcolm McLean]

"P" <sp************@yahoo.comwrote in message
news:11**********************@l70g2000hse.googlegr oups.com...

>I want to write a platform independent program that would use up at
least 5Gb of memory for testing purposes. How would I do that?

Thanks!

#include <stdio.h>
#include <stdlib.h>

char *encyclopedia;

int main(void)
{
encyclopedia = malloc(5 * 1024 * 1024 * 1024 );
if(!encyclopedia)
{
printf("Out of memory\n");
exit(EXIT_FAILURE);
}
gets(encyclopedia);
printf("Your encylopedia is %s\n", encyclopedia);
return 0;
}

However it is unlikely that you will be lucky enough to run on a platform
with 64 bit ints. So put casts to size_t and l suffixes etc into that
malloc() call until it seems to work.
There are two ways in which this program could fail, unrelated to the main
problem. One is obvious, but the reasoning gets a little hollow at times.
The other is more serious.

--
Free games and programming goodies.
http://www.personal.leeds.ac.uk/~bgy1mm

[santosh]

Malcolm McLean wrote:

>
"P" <sp************@yahoo.comwrote in message
news:11**********************@l70g2000hse.googlegr oups.com...

>>I want to write a platform independent program that would use up at
least 5Gb of memory for testing purposes. How would I do that?

Thanks!

#include <stdio.h>
#include <stdlib.h>

char *encyclopedia;

int main(void)
{
encyclopedia = malloc(5 * 1024 * 1024 * 1024 );

I suppose you didn't read the previous articles in this thread?

if(!encyclopedia)
{
printf("Out of memory\n");
exit(EXIT_FAILURE);
}
gets(encyclopedia);

No need to recommend dangerous functions to possible newbies.

printf("Your encylopedia is %s\n", encyclopedia);
return 0;
}

However it is unlikely that you will be lucky enough to run on a platform
with 64 bit ints. So put casts to size_t and l suffixes etc into that
malloc() call until it seems to work.

size_t is not guaranteed to be able to hold that value either.

[snip]

[Stephen Sprunk]

"jacob navia" <ja***@jacob.remcomp.frwrote in message
news:46**********************@news.orange.fr...

>
True. I should have added some test along the lines of
if (CHAR_BIT*sizeof(size_t) 33 && s = malloc(...);

That's not guaranteed to work either, even if there's 5GB of memory
available. size_t is only guaranteed to have at least 16 value bits; a
perverse implementation may have a 64-bit address space but a smaller
size_t, meaning you have to malloc() what you need in chunks no larger than
SIZE_MAX. The OP didn't specify he had to have his 5GB in a single
object...

However, I can't see any way a system could have 5GB of memory accessible if
(CHAR_BIT*sizeof(void *)) < 33. Of course, on most systems, sizeof(size_t)
== sizeof(void *), but the interesting cases are where that's not true.

S

--
Stephen Sprunk "Those people who think they know everything
CCIE #3723 are a great annoyance to those of us who do."
K5SSS --Isaac Asimov
--
Posted via a free Usenet account from http://www.teranews.com

[Ian Collins]

Stephen Sprunk wrote:

"jacob navia" <ja***@jacob.remcomp.frwrote in message
news:46**********************@news.orange.fr...

>>
True. I should have added some test along the lines of
if (CHAR_BIT*sizeof(size_t) 33 && s = malloc(...);

That's not guaranteed to work either, even if there's 5GB of memory
available. size_t is only guaranteed to have at least 16 value bits; a
perverse implementation may have a 64-bit address space but a smaller
size_t

How could it? size_t is defined as the result of the sizeof operator,
so the implementation would be limited to 64K objects. Perverse, but
possible I guess.

--
Ian Collins.

[¬a\\/b]

On Tue, 07 Aug 2007 08:57:41 +0200, "¬a\\/b" <[e-mail]:

this seems compilable in windows

#include <stdlib.h>
#include <stdio.h>
#include <windows.h>

int main(void)
{int i;
char *s[1024];

if(5*1024*1024<=1024 || 1024*1024<=0)
return 0;
for(i=0; i<1024; ++i)
{s[i]=malloc(5*1024*1024);
if(s[i]==0) break;
}
printf("Presa memoria=%gbytes i=%i\n",
i*1024.0*1024.0*5, i);
Sleep(12000);
printf("Esco\n");
if(i>0)
for(--i; i>=0; --i)
free(s[i]);
return 0;
}