From:	apsh AT ecr DOT mu DOT oz DOT au (Alistair_P SHILTON)
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Strange behaviour of new/delete
Date:	7 Jun 2000 07:27:55 GMT
Organization:	Computer Science, University of Melbourne
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Is that a no :) ?  Thanks anyway - its just that I've been trying to work this
out for ~4 weeks now with no success, so I thought, just maybe...  oh well,
back to the drawing board.  I'll try your suggestion of C++ing it up a bit
more and see if it helps.

Sorry for not posting the full code, but the program is quite large (~6000

over 4 files), and the new and delete statements are quite distant from one
another.

ps - how do you ckeck for new error?  Sorry if that's a dumb question, but
I'm relatively new to C++ (I usually do C).

Thanks again.


Martin Ambuhl (mambuhl AT earthlink DOT net) wrote:


: Alistair_P SHILTON wrote the text quoted below my answer:

:  /* mha: code posted by apsh AT ecr DOT mu DOT oz DOT au (Alistair_P SHILTON), turned
:     into a real program.  He is concerned with "Strange behaviour of
:     new/delete" and asks:

:     "I was wondering if anyone else has encountered trouble with
:     new/delete. I have a function which allocates memory with new as
:     follows:"

:     I have obviously added the 'int main() {' 'and return 0; }' program
:     bracketing.  All references to NULL have been changed to 0, in
:     conformance with most C++ prescriptive stylists, including BS.

:     a, b, c, i, removal, and size were never declared in the original
:     code. I have declared them as they appear, no matter whether this is
:     stylistically best. A value for i (5 in this case) and for size (12)
:     were arbitrarily added since it needs initialization.

:     I have included <cstdio> so the printfs become legal.

:     After all these things, to have a compilable program, there 
:     are no compilation or runtime errors.  Since the apsh's question now
:     has no referrent, I would suggest that his actual program (which he
:     has not shown us) has some apsh-generated errors, perhaps some of
:     which are corrected by the above.

:     The tests for new failure are misguided.  new does not act like 
:     malloc().  They have been removed.

:   */

: #include <cstdio>



: int main()
: {
:     double **res = new double *[3];
:     size_t i = 5, size = 12;
:     double *a = new double[i];
:     double *b = new double[1];
:     double *c = new double[size - i + 1];
:     res[0] = a;
:     res[1] = b;
:     res[2] = c;
:     double **removal = new double *[3];
:     removal[0] = a;
:     removal[1] = b;
:     removal[2] = c;
:     /* apsh - For simplicity, I've allocated 1 double too much to a and 
:        c.  Later on I delete as follows: (res has since become removal) 
:      */
:     delete removal[0];
:     printf("0 down\n");
:     delete removal[1];
:     printf("1 down\n");
:     delete removal[2];
:     printf("2 down\n");
:     printf("freed partial removal\n");
:     delete removal;
:     printf("free mem\n");
:     /* apsh: (ignore the printf's - I was debugging).  The odd
:        behaviour is this - if I don't actually use a or c (don't put
:        anything in them), then it hangs at delete removal[2] (even
:        though a non zero amount of memory was allocated)!! I've checked 
:        on unix, and it works fine - so is this a known bug with djgpp,
:        or am I missing something? */
:     /* mha: you are obviously missing something.  Perhaps it is legal
:        code. */
:     return 0;
: }






: > 
: > I was wondering if anyone else has encountered trouble with new/delete.
: > I have a function which allocates memory with new as follows:
: > 
: >     double **res;
: > 
: >     res = new double *[3];
: > 
: >     if ( res == NULL ) { return NULL; }
: > 
: >     a = new double[i];
: >     if ( a == NULL ) { return NULL; }
: > 
: >     b = new double[1];
: >     if ( b == NULL ) { return NULL; }
: > 
: >     c = new double[size-i+1];
: >     if ( c == NULL ) { return NULL; }
: > 
: >     res[0] = a;
: >     res[1] = b;
: >     res[2] = c;
: > 
: > For simplicity, I've allocated 1 double too much to a and c.  Later on I delete
: > as follows:
: > 
: > (res has since become removal)
: > 
: >         delete removal[0];
: > printf("0 down\n");
: >         delete removal[1];
: > printf("1 down\n");
: >         delete removal[2];
: > printf("2 down\n");
: > 
: > printf("freed partial removal\n");
: >         delete removal;
: > 
: > printf("free mem\n");
: > 
: > (ignore the printf's - I was debugging).  The odd behaviour is this - if I
: > don't actually use a or c (don't put anything in them), then it hangs at
: > delete removal[2] (even though a non zero amount of memory was allocated)!!
: > 
: > I've checked on unix, and it works fine - so is this a known bug with djgpp,
: > or am I missing something?
: > 
: > ----------------------------------------------------
: > 
: > Thanks
: > 
: > Alistair Shilton
: > 
: > http://www.ee.mu.oz.au/pgrad/apsh

: -- 
: Martin Ambuhl	mambuhl AT earthlink DOT net

: What one knows is, in youth, of little moment; they know enough who
: know how to learn. - Henry Adams

: A thick skin is a gift from God. - Konrad Adenauer

--
----------------------------------------------------

Alistair Shilton

http://www.ee.mu.oz.au/pgrad/apsh

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