If malloc fails what should I do?
1. Exit imediately.
2. Print an error message (or put a log entry) and exit.
3. Print an error message (or put a log entry) and continue
execution (after possibly recovering from the error).
Printing an error message might be difficult in a graphical environment.
--
mail to: randomzoo <at> spymac <dot> com 25  5064 
On Mon, 19 Jul 2004, H.A. Sujith wrote:
HS>If malloc fails what should I do?
HS>
HS>1. Exit imediately.
HS>2. Print an error message (or put a log entry) and exit.
HS>3. Print an error message (or put a log entry) and continue
HS>execution (after possibly recovering from the error).
That depends stronlgy on the concrete application. For one-shot programs
like 'ls' or so a malloc() failure is most probable a problem in the
environment and just printing a message (if possible) and exiting is the
best one can do. For programs that are long running or run under special
conditions (think of controlling software for a nuclear power plant) this
is not an option and they probably have to try to recover (and log, of
course).
HS>Printing an error message might be difficult in a graphical environment.
That's one of the reasons why such programs sometimes simply disappear
from the screen without any hint what happend.
harti
On Mon, 19 Jul 2004, H.A. Sujith wrote: If malloc fails what should I do?
1. Exit imediately.
Maybe.
2. Print an error message (or put a log entry) and exit.
Maybe.
3. Print an error message (or put a log entry) and continue
execution (after possibly recovering from the error).
Maybe.
The answer all depends on the situation. If IO absolutely must have a
successful malloc or there is not point continuing then I would exit. If
I'm attempt to allocate a large block of memory but can get by with a
smaller block then adjust and keep going.
Do I print an error message? Depends on the environment. If the program is
going to be used in an automated or embedded system then I would not print
an error message (there will be no human to see it). If the application is
always going to be run interactively then I would print an error message.
Printing an error message might be difficult in a graphical environment.
Why? If it is just because you have to go through the effort of creating a
dialog then learn to create a dialog. If it is because a failed malloc
means there isn't enough memory to display an error dialog, see if there
is a system level way of printing an error message. Often the OS will
reserve memory for printing critical error dialogs. If your OS does not do
this, allocate enough memory right at the start so there is memory to
print an error dialog. Keep that memory in reserve until you quit the
application.
--
Send e-mail to: darrell at cs dot toronto dot edu
Don't send e-mail to vi************@ whitehouse.gov
H.A. Sujith wrote: If malloc fails what should I do?
1. Exit imediately.
2. Print an error message (or put a log entry) and exit.
3. Print an error message (or put a log entry) and continue
execution (after possibly recovering from the error).
Printing an error message might be difficult in a graphical environment.
I have gone down the avenue of trying to make malloc() fail, and it's
easier said then done. Also, implementation specific settings have to
be set to create a possibility of malloc() failing. (e.g., RLIMIT_DATA
in linux, malloc.conf in BSD, etc.).
A good exercise would be just trying to get malloc() to fail under your
implementation to make sure the above items you listed even work. And
do not forget to allocate enough space for the trailing '\0'.
I have recently moved over to openBSD to experiment with making malloc()
fail. It's really implementation specific, so I'm curious what the
regulars here think about porting malloc() between platforms since there
doesn't seem to be a standard as to whether or not errno is set when
malloc() fails.
brian
"H.A. Sujith" wrote:
If malloc fails what should I do?
1. Exit imediately.
2. Print an error message (or put a log entry) and exit.
3. Print an error message (or put a log entry) and continue
execution (after possibly recovering from the error).
[...]
It depends entirely on the situation.
For example, I have a report generator program which allocates memory (in
chunks) for sorting the selected records. If malloc fails after I have
already allocated at least one memory block, then it doesn't matter, and
I simply stop trying to allocate more memory, and use only the memory
that I already have. In this case, the answer is:
4. Continue running, but without the memory you tried to allocate.
Of course, if the first malloc fails, then it's a fatal error.
--
+-------------------------+--------------------+-----------------------------+
| Kenneth J. Brody | www.hvcomputer.com | |
| kenbrody at spamcop.net | www.fptech.com | #include <std_disclaimer .h> |
+-------------------------+--------------------+-----------------------------+
H.A. Sujith a formulé la demande : If malloc fails what should I do?
1. Exit imediately.
2. Print an error message (or put a log entry) and exit.
3. Print an error message (or put a log entry) and continue
execution (after possibly recovering from the error).
Printing an error message might be difficult in a graphical environment.
There is no definitive answer, and it's beyond the C-language itself.
It's more a specification and eventually design issue.
-> At some library level, I tend to return some information that a
problem occured (null pointer, error value etc.)
-> At application level, I tend to display some message (to stderr,
stdout, some log file, a message box in graphical environment, ...).
The exit is an option if the error is not recoverable. You could simply
retry later, or with a smaller amout if it doesn't hurt.
But to conclude, and to come back to the C-language, a pointer with a
null value must not be dereferenced.
--
Emmanuel
"H.A. Sujith" <su****@localho st.localdomain> wrote If malloc fails what should I do?
1. Exit imediately.
2. Print an error message (or put a log entry) and exit.
3. Print an error message (or put a log entry) and continue
execution (after possibly recovering from the error).
Printing an error message might be difficult in a graphical environment.
It depends what you are allocating. If you are allocating a few bytes, maybe
for a filename, on a large system then basically malloc() cannot fail. The
system will have issued "low on memory" warnings long before this happens.
However for the program to be correct, you still need to handle the failure.
Exit is perfectly reasonable.
However if you are allocating a very large data set, it is entirely possible
that the computer is genuinely out of memory. So you need to tell the user
what has happened, and allow him to close other applications and retry, or
do whatever else is necessary to recover.
On 19 Jul 2004 08:45:18 -0700, in comp.lang.c , "H.A. Sujith"
<su****@localho st.localdomain> wrote: If malloc fails what should I do?
Whatever is most appropriate for your application.
1. Exit imediately.
2. Print an error message (or put a log entry) and exit.
neither very suitable for pacemakers, air traffic control systems etc.....
typically more ok for simple tools eg cat, cp.
3. Print an error message (or put a log entry) and continue
execution (after possibly recovering from the error).
may not be possible, but graceful cleanup is advisable.
Printing an error message might be difficult in a graphical environment.
There's usually a system-specific way to flag fatal errors which uses
reserved system memory and is thus not subject to your own malloc woe.
--
Mark McIntyre
CLC FAQ <http://www.eskimo.com/~scs/C-faq/top.html>
CLC readme: <http://www.angelfire.c om/ms3/bchambless0/welcome_to_clc. html>
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In article <sl************ *******@localho st.localdomain> ,
"H.A. Sujith" <su****@localho st.localdomain> wrote: If malloc fails what should I do?
1. Exit imediately.
2. Print an error message (or put a log entry) and exit.
3. Print an error message (or put a log entry) and continue
execution (after possibly recovering from the error).
Printing an error message might be difficult in a graphical environment.
You look at it from the programmer's point of view. You should look at
it from the user's point of view. What are the consequences for the user
of your software of your action? What can you do or what do you have to
do to improve these consequences?
If I spent twelve hours editing a document, choose "Save" from a menu,
and the program runs out of memory just at this point and exits (after
printing an error message or not) without saving twelve hours of my
work, then the programmer responsible deserves to be shot.
"Malcolm" <ma*****@55bank .freeserve.co.u k> writes: "H.A. Sujith" <su****@localho st.localdomain> wrote If malloc fails what should I do?
1. Exit imediately.
2. Print an error message (or put a log entry) and exit.
3. Print an error message (or put a log entry) and continue
execution (after possibly recovering from the error).
Printing an error message might be difficult in a graphical environment.
If you're in a graphical environment, presumably you have some way of
displaying a message, perhaps by popping up a dialog window.
It depends what you are allocating. If you are allocating a few bytes, maybe
for a filename, on a large system then basically malloc() cannot fail. The
system will have issued "low on memory" warnings long before this happens.
You're assuming that malloc() will fail only if the entire system is
running low on memory. Many systems place limits on the memory
allocated by a single program; a program can hit those limits long
before the system as a whole is in trouble.
Even if the entire system is running low on memory, it's unlikely that
a given program will be aware of any "low on memory" warnings that the
system might have generated. If the system has 10 bytes left to
allocate, and a program asks for 20, the allocation will fail.
Obviously a large request is more likely to fail than a small one, but
it's always possible that a 1-byte request will be the straw that
breaks the camel's back.
As for recovery strategies, it's seldom sensible for a program to try
to continue whatever task it was working on after a malloc() failure.
Whether aborting the task means aborting the entire program depends on
the nature of the program.
If the program has built up a lot of valuable information, it should
try to save it before aborting. (For example, if a text editor
doesn't have enough memory to insert another character into the
buffer, it shouldn't bail out and throw away the whole buffer.)
There is no universal answer.
--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
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