[prog] Segmentation fault :-(

[Conor Daly]

On Tue, Sep 24, 2002 at 06:06:57PM +1000 or thereabouts, Jacinta Richardson wrote:
> 
> Something else to try is to add the following:
> 
> /* at the top of your program */
> #include <assert.h>
> 
> /* then */
> if (GetStatus() != SOCK_HS_SUCCESS)
> {
>     assert(data != NULL);
>     return BaseSocket::Receive(data, dataLen, flags);
> }
> 
> assert.h provides the assert function.  If the test is false it'll kill
> your program and provide you a useful error message.  I found it a very
> handy debugging technique.  Much tidier than:
> if(data == NULL)
> {
>      fprintf(STDERR, "data is NULL at line 1234\n";
>      exit(1);
> }
> especially because it saves you from worrying about moving line numbers.
> ;)

Another thing to remember, IIRC, is that printf() and fprintf() are often
asynchronous.  The printf() inside the "BaseSocket::Receive()" function may
happen but the program segfaults _before_ the buffer is flushed to the
console.  I'm not entirely sure about that but I seem to remember suffering
for it in the past...  Adding a fflush(stdout); after the printf() might
help there.  However, AIUI, assert() is not subject to the same limitation.

I was going to post this link to the list anyhow but it seems relevant here.

http://www.iol.ie/~padraiga/backtrace.c

backtrace.c is a little something that traps (user specified) signals and
syslogs (CRIT) the last 7 function calls and tries to dump core.  Apparently it
has little/no overhead when running and is therefore suitable for inclusion
in release versions.  It requires glibc.

Conor
-- 
Conor Daly 
Met Eireann, Glasnevin Hill, Dublin 9, Ireland
Ph +353 1 8064276 Fax +353 1 8064247
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