calloc()

[Michael McGarry]

Hi,

What would cause calloc() to return a NULL pointer?

Is the system simply out of memory?

Regards,

Michael

[Default User]

Michael McGarry wrote:

Hi,

What would cause calloc() to return a NULL pointer?

Is the system simply out of memory?

It's unlikely to be out. However, it may not have a piece available to
your program that is large enough to fill the request.


Brian

[Michael McGarry]

Is there anything I can do to fix that?

I guess if there is not contiguous memory of the size I need I am out
of luck?

Thanks for any help,

Michael

Default User wrote:

Michael McGarry wrote:

Hi,

What would cause calloc() to return a NULL pointer?

Is the system simply out of memory?

It's unlikely to be out. However, it may not have a piece available to
your program that is large enough to fill the request.


Brian

[Ian Collins]

Michael McGarry wrote:

>
Default User wrote:

>>Michael McGarry wrote:

>>>Hi,

What would cause calloc() to return a NULL pointer?

Is the system simply out of memory?

It's unlikely to be out. However, it may not have a piece available to
your program that is large enough to fill the request.

Is there anything I can do to fix that?

I guess if there is not contiguous memory of the size I need I am out
of luck?

Thanks for any help,

Please don't top post.

Assuming you implementation has errno, you should test its value after
the failing call to determine the cause of the failure.

If there isn't contiguous memory of the size you need, you are out of
luck and should consider a different design. As an alternative, try
allocating the bigger memory blocks earlier.

--
Ian Collins.

[Joe Wright]

Michael McGarry wrote:

Hi,

What would cause calloc() to return a NULL pointer?

Is the system simply out of memory?

Regards,

Michael

Something like that. Given rational arguments, malloc, calloc and
realloc seldom error out. But you can stress them. For example size_t is
an unsigned 32-bit type on my system. calloc multiplies its two size_t
arguments to come up with size. If these two are not chosen with some
sanity, calloc will barf because I don't have anything near 2^64 bytes
of memory to address.

--
Joe Wright
"Everything should be made as simple as possible, but not simpler."
--- Albert Einstein ---

[Keith Thompson]

Ian Collins <ia******@hotma il.comwrites:

Michael McGarry wrote:

>Default User wrote:

>>>Michael McGarry wrote:
What would cause calloc() to return a NULL pointer?

Is the system simply out of memory?

It's unlikely to be out. However, it may not have a piece available to
your program that is large enough to fill the request.

Is there anything I can do to fix that?

I guess if there is not contiguous memory of the size I need I am out
of luck?

Thanks for any help,

Please don't top post.

Assuming you implementation has errno, you should test its value after
the failing call to determine the cause of the failure.

His implementation certainly has error if it's a conforming hosted
implementation. But the standard doesn't say that malloc() sets errno
on a failure. And even if it does, it's not likely to distinguish
between different forms of "not enough memory".

If there isn't contiguous memory of the size you need, you are out of
luck and should consider a different design. As an alternative, try
allocating the bigger memory blocks earlier.

Some systems impose limits on how much memory a given program (or
process, or user, or whatever) can allocate. You may or may not be
able to increase that limit; the details are system-specific.

It's also possible that you haven't run out of available memory,
rather than you've done something to mess up the system's internal
data structures.

Incidentally, calloc() isn't necessarily more useful than the simpler
malloc(); calloc() initializes the allocated memory to all-bits-zero,
but that's not necessarily as useful as you might think. In
particular, neither floating-point 0.0 nor null pointers are
guaranteed to be represented as all-bits-zero.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.
u

[Default User]

Michael McGarry wrote:

Default User wrote:

Michael McGarry wrote:

Hi,
>
What would cause calloc() to return a NULL pointer?
>
Is the system simply out of memory?

It's unlikely to be out. However, it may not have a piece available
to your program that is large enough to fill the request.

Don't top-post, text rearranged.

Is there anything I can do to fix that?

I guess if there is not contiguous memory of the size I need I am out
of luck?

Pretty much. However, it's not a common occurrence for modern systems.
Is this theoretical, or an actual problem you've encountered?


Brian

[Ian Collins]

Keith Thompson wrote:

Ian Collins <ia******@hotma il.comwrites:

>>Michael McGarry wrote:

>>>Default User wrote:

Michael McGarry wrote:

>What would cause calloc() to return a NULL pointer?
>
>Is the system simply out of memory?

It's unlikely to be out. However, it may not have a piece available to
your program that is large enough to fill the request.
Is there anything I can do to fix that?

I guess if there is not contiguous memory of the size I need I am out
of luck?

Thanks for any help,

Please don't top post.

Assuming you implementation has errno, you should test its value after
the failing call to determine the cause of the failure.

His implementation certainly has error if it's a conforming hosted
implementation.

I was careful not to make that assumption.

But the standard doesn't say that malloc() sets errno
on a failure. And even if it does, it's not likely to distinguish
between different forms of "not enough memory".

True, but all it takes is a quick read of the platform's documentation
to see if it does. Solaris and I think Linux makes the distinction.

>

>>If there isn't contiguous memory of the size you need, you are out of
luck and should consider a different design. As an alternative, try
allocating the bigger memory blocks earlier.

Some systems impose limits on how much memory a given program (or
process, or user, or whatever) can allocate. You may or may not be
able to increase that limit; the details are system-specific.

If you know your allocation is within these bounds, there's a pretty
good chance you have run into a fragmentation issue, so my suggestion is
still worth investigation.

--
Ian Collins.

[Flash Gordon]

Ian Collins wrote:

Michael McGarry wrote:

>Default User wrote:

>>Michael McGarry wrote:
Hi,

What would cause calloc() to return a NULL pointer?

Is the system simply out of memory?
It's unlikely to be out. However, it may not have a piece available to
your program that is large enough to fill the request.

Is there anything I can do to fix that?

I guess if there is not contiguous memory of the size I need I am out
of luck?

Thanks for any help,

Please don't top post.

Assuming you implementation has errno,

If it is a hosted C implementation then it has errno.

you should test its value after
the failing call to determine the cause of the failure.

The standard does not require that errno be set. The Unix98 standard
requires that it be set to ENOMEM on failure if the linux documentation
is accurate, but if it is always set to ENOMEM on failure that gives you
no additional information.

In other words, checking errno in this instance is pointless on at least
one implementation and quite likely pointless on a number of others.

If there isn't contiguous memory of the size you need, you are out of
luck and should consider a different design. As an alternative, try
allocating the bigger memory blocks earlier.

This is better advice. I would also suggest checking for memory leaks
and making sure you are passing sensible numbers to calloc.
--
Flash Gordon
Still sigless on this computer.

[Richard]

Ian Collins <ia******@hotma il.comwrites:

Keith Thompson wrote:

>Ian Collins <ia******@hotma il.comwrites:

>>>Michael McGarry wrote:

Default User wrote:

>Michael McGarry wrote:
>
>>What would cause calloc() to return a NULL pointer?
>>
>>Is the system simply out of memory?
>
>It's unlikely to be out. However, it may not have a piece available to
>your program that is large enough to fill the request.
>

Is there anything I can do to fix that?

I guess if there is not contiguous memory of the size I need I am out
of luck?

Thanks for any help,
Please don't top post.

Assuming you implementation has errno, you should test its value after
the failing call to determine the cause of the failure.

His implementation certainly has error if it's a conforming hosted
implementation .

I was careful not to make that assumption.

>But the standard doesn't say that malloc() sets errno
on a failure. And even if it does, it's not likely to distinguish
between different forms of "not enough memory".

True, but all it takes is a quick read of the platform's documentation
to see if it does. Solaris and I think Linux makes the distinction.

Would Linux, in default, ever return NULL? The default is to return
pointers to memory that is not even available : optimistic
strategy. Yuck :) I might, time allowing, knock up a program to fragment
up the memory and then try a huge alloc.

Q: does the swapfile come on "seamlessly " on most platforms here? In
which case would we ever see malloc failing assuming enough swap? How
does that work (yes I know OT)? Even if the swap is fragmented is the
memory block contiguous?