malloc error checking

[Marlene Stebbins]

At one point in my program I have about a dozen calls to malloc. I want
to check for malloc failure, but I don't want to write:

if((buffer_x = malloc(BUFSIZE * sizeof(*buffer_ x))) == NULL)
{
exit(EXIT_FAILU RE);
fprintf(stderr, "malloc failed");
}

for each individual call if there is a stylistically better way. How
would this be handled in commercial code?

[David REsnick]

Re: malloc error checking

Marlene Stebbins wrote:
[color=blue]
> At one point in my program I have about a dozen calls to malloc. I want
> to check for malloc failure, but I don't want to write:
>
> if((buffer_x = malloc(BUFSIZE * sizeof(*buffer_ x))) == NULL)
> {
> exit(EXIT_FAILU RE);
> fprintf(stderr, "malloc failed");
> }
>
> for each individual call if there is a stylistically better way. How
> would this be handled in commercial code?[/color]

Standard way is to write a wrapper you call in place of malloc
when you want this behavior. e.g.

void *safe_malloc(si ze_t size)
{
void *ret = malloc(size);
if (ret == NULL) {
fprintf(stderr, "malloc %u bytes failed", (unsigned)size) ;
exit(EXIT_FAILU RE);
}

return ret;
}

That also has the advantage of letting you decide what to do on
malloc(0)... No guarantee the printf will work with no memory
available either, mind you. I added the size to your printf
and put it before the exit :) The size is useful in case a programming
error causes you to try to malloc(-1) or some such.

-David

[Kornilios Kourtis]

Re: malloc error checking

Marlene Stebbins <marlene@mail.c om> wrote:[color=blue]
> At one point in my program I have about a dozen calls to malloc. I want
> to check for malloc failure, but I don't want to write:
>
> if((buffer_x = malloc(BUFSIZE * sizeof(*buffer_ x))) == NULL)
> {
> exit(EXIT_FAILU RE);
> fprintf(stderr, "malloc failed");[/color]
^^^^^^^^^^^^^
this message will never be printed
because it's after the exit() call
[color=blue]
> }
>[/color]
[color=blue]
> for each individual call if there is a stylistically better way. How
> would this be handled in commercial code?[/color]

You can use another wrapper function:

void *malloc_wrap(si ze_t size)
{
void *ret;

ret = malloc(size);
if (ret == NULL){
fprintf(stderr, "malloc failed\n");
exit(EXIT_FAULU RE);
}

return ret;
}

--
Kornilios Kourtis

Computers are useless. They can only give you answers.
- Pablo Picasso

[Michael Mair]

Re: malloc error checking


David REsnick wrote:[color=blue]
> Marlene Stebbins wrote:
>[color=green]
>> At one point in my program I have about a dozen calls to malloc. I
>> want to check for malloc failure, but I don't want to write:
>>
>> if((buffer_x = malloc(BUFSIZE * sizeof(*buffer_ x))) == NULL)
>> {
>> exit(EXIT_FAILU RE);
>> fprintf(stderr, "malloc failed");
>> }
>>
>> for each individual call if there is a stylistically better way. How
>> would this be handled in commercial code?[/color]
>
>
> Standard way is to write a wrapper you call in place of malloc
> when you want this behavior. e.g.
>
> void *safe_malloc(si ze_t size)
> {
> void *ret = malloc(size);
> if (ret == NULL) {
> fprintf(stderr, "malloc %u bytes failed", (unsigned)size) ;
> exit(EXIT_FAILU RE);
> }
>
> return ret;
> }
>
> That also has the advantage of letting you decide what to do on
> malloc(0)... No guarantee the printf will work with no memory
> available either, mind you. I added the size to your printf
> and put it before the exit :) The size is useful in case a programming
> error causes you to try to malloc(-1) or some such.[/color]

Note: Under C89, casting to unsigned long (and using %lu) is safer, as
we do not know how wide size_t actually is. We still might have the
situation that (size_t)((unsig ned long)((size_t) -1)) != (size_t) -1.
Under C99 or with a C99 compliant standard library, use the length
modifier for size_t (z, i.e. %zu).


Cheers
Michael
--
E-Mail: Mine is a gmx dot de address.

[Rouben Rostamian]

Re: malloc error checking

In article <GWUAd.617669$n l.442454@pd7tw3 no>,
Marlene Stebbins <marlene@mail.c om> wrote:[color=blue]
>At one point in my program I have about a dozen calls to malloc. I want
>to check for malloc failure, but I don't want to write:
>
> if((buffer_x = malloc(BUFSIZE * sizeof(*buffer_ x))) == NULL)
> {
> exit(EXIT_FAILU RE);
> fprintf(stderr, "malloc failed");
> }
>
>for each individual call if there is a stylistically better way. How
>would this be handled in commercial code?[/color]

If all these calls occur within the body of a single function, then
you may do:


x1 = malloc(whatever );
x2 = malloc(whatever );
...
xn = malloc(whatever );

if (!x1 || !x2 || ... || !xn) {
fprintf(stderr, "malloc failed");
exit(EXIT_FAILU RE);
}

--
Rouben Rostamian

[Marlene Stebbins]

Re: malloc error checking

Marlene Stebbins wrote:[color=blue]
> At one point in my program I have about a dozen calls to malloc. I want
> to check for malloc failure, but I don't want to write:
>
> if((buffer_x = malloc(BUFSIZE * sizeof(*buffer_ x))) == NULL)
> {
> exit(EXIT_FAILU RE);
> fprintf(stderr, "malloc failed");
> }[/color]

I just noticed that I've got the exit and fprintf statements bass
ackwards. I should have had another cup of coffee before posting this.

MS

[Emmanuel Delahaye]

Re: malloc error checking

David REsnick wrote on 30/12/04 :[color=blue]
> void *safe_malloc(si ze_t size)
> {
> void *ret = malloc(size);
> if (ret == NULL) {
> fprintf(stderr, "malloc %u bytes failed", (unsigned)size) ;
> exit(EXIT_FAILU RE);
> }
>
> return ret;
> }[/color]

I would amend this code this way:

/* interface (.h) */

#define safe_malloc(siz e) \
safe_malloc_ (size, __FILE__, __LINE__)

void *safe_malloc_ (size_t size, char const *file, int line);


/* implementation (.c) */

void *safe_malloc_ (size_t size, char const *file, int line)
{
void *p = malloc(size);

if (p == NULL)
{
fprintf (stderr
, "malloc %lu bytes failed at %s:%d\n"
, (unsigned long)size
, file
, line
);
exit (EXIT_FAILURE);
}
return ret;
}

--
Emmanuel
The C-FAQ: http://www.eskimo.com/~scs/C-faq/faq.html
The C-library: http://www.dinkumware.com/refxc.html

"C is a sharp tool"

[Eric Sosman]

Re: malloc error checking

Marlene Stebbins wrote:
[color=blue]
> At one point in my program I have about a dozen calls to malloc. I want
> to check for malloc failure, but I don't want to write:
>
> if((buffer_x = malloc(BUFSIZE * sizeof(*buffer_ x))) == NULL)
> {
> exit(EXIT_FAILU RE);
> fprintf(stderr, "malloc failed");
> }
>
> for each individual call if there is a stylistically better way. How
> would this be handled in commercial code?[/color]

"It depends." Here are a few patterns:

if ((buff1 = malloc(size1)) == NULL
|| (buff2 = malloc(size2)) == NULL
...
|| (buff12 = malloc(size12)) == NULL) {
die_horribly();
}


for (i = 0; i < 12; ++i) {
if ((buff[i] = malloc(size[i])) == NULL)
die_horribly();
}


/* malloc_wrapper( ) dies horribly on failure */
buff1 = malloc_wrapper( size1);
buff2 = malloc_wrapper( size2);
...
buff12 = malloc_wrapper( size12);


char *allbuffs = malloc(size1 + size2 + ... + size12);
if (allbuffs == NULL)
die_horribly();
buff1 = (Type1*)allbuff s;
buff2 = (Type2*)(allbuf fs + size1);
...
buff12 = (Type12*)(allbu ffs + size1 + size2 + ... + size11);

.... and many, many more.

There are at least two lessons in all this. First, there
are manymanymany ways to organize the handling of failures and
exceptional conditions in a program. Second, the choice of
method is usually not driven by the nature of the failure, but
by the structure of the program.

--
Eric Sosman
esosman@acm-dot-org.invalid

[Jonathan Burd]

Re: malloc error checking

Emmanuel Delahaye wrote:[color=blue]
> David REsnick wrote on 30/12/04 :
>[color=green]
>> void *safe_malloc(si ze_t size)
>> {
>> void *ret = malloc(size);
>> if (ret == NULL) {
>> fprintf(stderr, "malloc %u bytes failed", (unsigned)size) ;
>> exit(EXIT_FAILU RE);
>> }
>>
>> return ret;
>> }[/color]
>
>
> I would amend this code this way:
>
> /* interface (.h) */
>
> #define safe_malloc(siz e) \
> safe_malloc_ (size, __FILE__, __LINE__)
>
> void *safe_malloc_ (size_t size, char const *file, int line);
>
>
> /* implementation (.c) */
>
> void *safe_malloc_ (size_t size, char const *file, int line)
> {
> void *p = malloc(size);
>
> if (p == NULL)
> {
> fprintf (stderr
> , "malloc %lu bytes failed at %s:%d\n"
> , (unsigned long)size
> , file
> , line
> );
> exit (EXIT_FAILURE);
> }[/color]

ret isn't defined. He means return p, anyway.[color=blue]
> return ret;
> }
>[/color]

[Emmanuel Delahaye]

Re: malloc error checking

(supersedes <mn.f4417d4c83f e5bea.15512@YOU RBRAnoos.fr>)

David REsnick wrote on 30/12/04 :[color=blue]
> void *safe_malloc(si ze_t size)
> {
> void *ret = malloc(size);
> if (ret == NULL) {
> fprintf(stderr, "malloc %u bytes failed", (unsigned)size) ;
> exit(EXIT_FAILU RE);
> }
>
> return ret;
> }[/color]

I would amend this code this way:

/* interface (.h) */

#define safe_malloc(siz e) \
safe_malloc_ (size, __FILE__, __LINE__)

void *safe_malloc_ (size_t size, char const *file, int line);

/* implementation (.c) */

void *safe_malloc_ (size_t size, char const *file, int line)
{
void *p = malloc(size);

if (p == NULL)
{
fprintf (stderr
, "malloc %lu bytes failed at %s:%d\n"
, (unsigned long)size
, file
, line
);
exit (EXIT_FAILURE);
}
return p;
}

--
Emmanuel
The C-FAQ: http://www.eskimo.com/~scs/C-faq/faq.html
The C-library: http://www.dinkumware.com/refxc.html

"Clearly your code does not meet the original spec."
"You are sentenced to 30 lashes with a wet noodle."
-- Jerry Coffin in a.l.c.c++

[Emmanuel Delahaye]

Re: malloc error checking

Jonathan Burd wrote on 31/12/04 :[color=blue][color=green]
>> void *safe_malloc_ (size_t size, char const *file, int line)
>> {
>> void *p = malloc(size);[/color][/color]

<...>
[color=blue]
> ret isn't defined. He means return p, anyway.[color=green]
>> return ret;
>> }
>>[/color][/color]

Absolutely. Correction made.

return p;

--
Emmanuel
The C-FAQ: http://www.eskimo.com/~scs/C-faq/faq.html
The C-library: http://www.dinkumware.com/refxc.html

"Mal nommer les choses c'est ajouter du malheur au
monde." -- Albert Camus.

[Artie Gold]

Re: malloc error checking

Emmanuel Delahaye wrote:[color=blue]
> (supersedes <mn.f4417d4c83f e5bea.15512@YOU RBRAnoos.fr>)
>
> David REsnick wrote on 30/12/04 :
>[color=green]
>> void *safe_malloc(si ze_t size)
>> {
>> void *ret = malloc(size);
>> if (ret == NULL) {
>> fprintf(stderr, "malloc %u bytes failed", (unsigned)size) ;
>> exit(EXIT_FAILU RE);
>> }
>>
>> return ret;
>> }[/color]
>
>
> I would amend this code this way:
>
> /* interface (.h) */
>
> #define safe_malloc(siz e) \
> safe_malloc_ (size, __FILE__, __LINE__)
>
> void *safe_malloc_ (size_t size, char const *file, int line);
>
> /* implementation (.c) */
>
> void *safe_malloc_ (size_t size, char const *file, int line)
> {
> void *p = malloc(size);
>
> if (p == NULL)
> {
> fprintf (stderr
> , "malloc %lu bytes failed at %s:%d\n"
> , (unsigned long)size
> , file
> , line
> );[/color]

Ooooh. Not a great idea. If malloc() fails, fprintf (which likely uses
malloc() itself) may also fail.
[color=blue]
> exit (EXIT_FAILURE);
> }
> return p;
> }
>[/color]
HTH,
--ag

--
Artie Gold -- Austin, Texas
http://it-matters.blogspot.com (new post 12/5)

http://www.cafepress.com/goldsays

[Emmanuel Delahaye]

Re: malloc error checking

Artie Gold wrote on 01/01/05 :[color=blue][color=green]
>> void *safe_malloc_ (size_t size, char const *file, int line)
>> {
>> void *p = malloc(size);
>>
>> if (p == NULL)
>> {
>> fprintf (stderr
>> , "malloc %lu bytes failed at %s:%d\n"
>> , (unsigned long)size
>> , file
>> , line
>> );[/color]
>
> Ooooh. Not a great idea. If malloc() fails, fprintf (which likely uses
> malloc() itself) may also fail.[/color]

Do you have any evidence of this ? Do you meant that the only option is

exit(EXIT_FAILU RE);

--
Emmanuel
The C-FAQ: http://www.eskimo.com/~scs/C-faq/faq.html
The C-library: http://www.dinkumware.com/refxc.html

"Clearly your code does not meet the original spec."
"You are sentenced to 30 lashes with a wet noodle."
-- Jerry Coffin in a.l.c.c++

[Chris Croughton]

Re: malloc error checking

On Fri, 31 Dec 2004 22:23:46 -0600, Artie Gold
<artiegold@aust in.rr.com> wrote:
[color=blue]
> Emmanuel Delahaye wrote:[color=green]
>>
>> void *safe_malloc_ (size_t size, char const *file, int line)
>> {
>> void *p = malloc(size);
>>
>> if (p == NULL)
>> {
>> fprintf (stderr
>> , "malloc %lu bytes failed at %s:%d\n"
>> , (unsigned long)size
>> , file
>> , line
>> );[/color]
>
> Ooooh. Not a great idea. If malloc() fails, fprintf (which likely uses
> malloc() itself) may also fail.[/color]

And the ceiling may fall in and crush the hard disk. That isn't a good
reason to not output diagnostics. What would you suggest instead?
Just:
[color=blue][color=green]
>> exit (EXIT_FAILURE);[/color][/color]

with no explanation?

(There are many occasions when malloc may fail but fprintf will work
fine -- when the I/O buffers are already allocated, when the size
requested is unreasonably big, etc. If fprintf does fail, it is likely
to do so with a code dump which can be inspected, whereas just doing
exit will not be trapped.)

Chris C

[Artie Gold]

Re: malloc error checking

Chris Croughton wrote:[color=blue]
> On Fri, 31 Dec 2004 22:23:46 -0600, Artie Gold
> <artiegold@aust in.rr.com> wrote:
>
>[color=green]
>>Emmanuel Delahaye wrote:
>>[color=darkred]
>>>void *safe_malloc_ (size_t size, char const *file, int line)
>>>{
>>> void *p = malloc(size);
>>>
>>> if (p == NULL)
>>> {
>>> fprintf (stderr
>>> , "malloc %lu bytes failed at %s:%d\n"
>>> , (unsigned long)size
>>> , file
>>> , line
>>> );[/color]
>>
>>Ooooh. Not a great idea. If malloc() fails, fprintf (which likely uses
>>malloc() itself) may also fail.[/color]
>
>
> And the ceiling may fall in and crush the hard disk. That isn't a good
> reason to not output diagnostics. What would you suggest instead?
> Just:
>
>[color=green][color=darkred]
>>> exit (EXIT_FAILURE);[/color][/color]
>
>
> with no explanation?[/color]

Point taken.
[color=blue]
>
> (There are many occasions when malloc may fail but fprintf will work
> fine -- when the I/O buffers are already allocated, when the size
> requested is unreasonably big, etc. If fprintf does fail, it is likely
> to do so with a code dump which can be inspected, whereas just doing
> exit will not be trapped.)
>[/color]
It's one of those situations where going into platform-specific-land
(using lower level calls) *may* be indicated. But again, I concede your
point.

--ag
--
Artie Gold -- Austin, Texas
http://it-matters.blogspot.com (new post 12/5)

http://www.cafepress.com/goldsays