Strange error when reallocating memory

[francesco]

I get this strange error message


subsets.exe: malloc.c:2451: sYSMALLOc: Assertion `(old_top == (((mbinptr)
(((char *) &((av)->bins[((1) - 1) * 2])) - __builtin_offsetof (struct
malloc_chunk, fd)))) && old_size == 0) || ((unsigned long) (old_size) >=
(unsigned long)((((__builtin_offsetof (struct malloc_chunk, fd_nextsize))
+((2 * (sizeof(size_t))) - 1)) & ~((2 * (sizeof(size_t))) - 1))) &&
((old_top)->size & 0x1) && ((unsigned long)old_end & pagemask) == 0)'
failed.

The program works correcly for a certain numbers of data, say n=7, when I
try it for n>7, I get this error message.

I need to dinamically allocate memory for 2^n structs. It workd properly
until I try the program for n=8 or greater, then it fails.

Francesco

 

[Ian Collins]

I get this strange error message


subsets.exe: malloc.c:2451: sYSMALLOc: Assertion `(old_top == (((mbinptr)
(((char *) &((av)->bins[((1) - 1) * 2])) - __builtin_offsetof (struct
malloc_chunk, fd)))) && old_size == 0) || ((unsigned long) (old_size) >=
(unsigned long)((((__builtin_offsetof (struct malloc_chunk, fd_nextsize))
+((2 * (sizeof(size_t))) - 1)) & ~((2 * (sizeof(size_t))) - 1))) &&
((old_top)->size & 0x1) && ((unsigned long)old_end & pagemask) == 0)'
failed.

The program works correcly for a certain numbers of data, say n=7, when I
try it for n>7, I get this error message.

I need to dinamically allocate memory for 2^n structs. It workd properly
until I try the program for n=8 or greater, then it fails.

You have an error at line 42.

 

[francesco]

You have an error at line 42.

Sorry, this is he code

#include<stdlib.h>
#include<stdio.h>
typedef struct {
int *ptrSet;
int elementi;
}Set;
int pot(int base,int esponente);
void stamparesti( int *resti, int n);
int main()
{
Set *ptrPDS=NULL;
int *ptr2Set=NULL;
int *resti=NULL;
int *set=NULL;
int n,m;
int i=0,j=0;
int N,Q=0;
int card=0;
printf("Inserisci il numero di elementi di S\n");
scanf("%d",&n);
m=pot(2,n);
printf("L'insieme dei sottoinsiemi di un insieme S ha %d sottoinsiemi
\n",m);
ptrPDS=(Set *)malloc(sizeof(Set)*m);
if(ptrPDS==NULL)
{
printf("Impossibile allocare spazio per l'insieme PDS: memoria
insufficiente\n");
free(ptrPDS);
exit(1);
}
set=malloc(sizeof(int)*n);
// Verifica se esiste abbastanza memoria per l'allocazione dell'insieme
if(set==NULL)
{
printf("Impossibile allocare spazio per l'insieme S: memoria
insufficiente\n");
free(set);
exit(1);
}

printf("Iserire gli elementi di S\n");
for(i=0;i<n;i++)
{
printf("\nInserire elemento %d",i);scanf("%d",set+i);
}
for(i=0;i<m;i++)
{
printf("i=%d\n",i);
resti=malloc(sizeof(int)*n);
if(resti==NULL)
{
printf("Impossibile allocare spazio per l'insieme S:
memoria insufficiente\n");
free(resti);
exit(1);
}
N=i;
//Conversione in binario del numero i
for(j=0;j<n;j++)
{
Q=N/2;
*(resti+j)=N%2;
N=Q;
}
stamparesti(resti,n);
ptr2Set=malloc(sizeof(int));
if(ptr2Set==NULL)
{
printf("Allocazione di memoria non riuscita\n");
free(ptr2Set);
exit(1);
}
card=0;
for(j=0;j<n;j++)
{
printf("j=%d card=%d\t",j,card);
if(*(resti+j)==1)
{
ptr2Set=realloc(ptr2Set,++card);
if(ptr2Set==NULL)
{
printf("Allocazione di memoria non riuscita\n");
free(ptr2Set);
exit(1);
}
*(ptr2Set+card-1)=*(set+j);
}
}
free(resti);
(ptrPDS+i)->elementi=card;
(ptrPDS+i)->ptrSet=ptr2Set;
printf("i=%d\telementi=%d\tptrSet=%p\n",i,card,ptr2Set);
}
// Stampa elementi sottoinsieme.
for(i=0;i<m;i++)
{
ptr2Set=(ptrPDS+i)->ptrSet;
printf("S%d={",i);
card=(ptrPDS+i)->elementi;
if (card==0) printf("}\n");
else
{
for(j=0;j<card-1;j++) printf("%d,",*(ptr2Set+j));
printf("%d}\n",*(ptr2Set+j));
}
printf("\n");

}
free(ptrPDS);
free(ptr2Set);
free(set);
return 0;
}
// Funzione per il calcolo della potenza di un numero intero n ad un
esponente
int pot(int base,int esponente)
{
int p=1;
int i=0;
while(i++<esponente)
p=p*base;
return p;
}
// Stampa dei resti
void stamparesti( int *resti, int n)
{
int j;
for(j=0;j<n;j++)
{
printf("\t%d",*(resti+j));
}
printf("\n");
}


I use Open Suse Linux 12.2, gcc compiler 4.7.1


Francesco

 

[BartC]

ptr2Set=malloc(sizeof(int));

Should this be:
ptr2Set=malloc(sizeof(int)*n);
?

(BTW the layout of your code could be improved!)

 

[Eric Sosman]

[...]
ptr2Set=realloc(ptr2Set,++card);

ptr2set = realloc(ptr2set, ++card * sizeof(int));

Better,

ptr2set = realloc(ptr2set, ++card * sizeof *ptr2set);

Other improvements are possible, and there may be other
problems. Start by fixing this one, and see how far you get.

 

[Rosario1903]

Sorry, this is he code

tu scrivi qualcosa come
v=malloc(200000);
if(v==NULL)
{free(v);
return 0;
}

mentre e sufficiente scrivere
v=malloc(200000);
if(v==NULL) return 0;

poiche' se v == 0 allora v non punta a memoria
da liberare... cmq free(v) quando v==0 non reca danni
solo: perche' scriverlo se non è necessario?

per il resto, quando ho visto m=2^n e m usato come parametro
per malloc ed come parametro per il ciclo for: ho abbandonato...

 

[Phil Carmody]

Sorry, this is he code

#include<stdlib.h>
#include<stdio.h>
typedef struct {
int *ptrSet;

Fix your indentation (might be a news client issue).

int elementi;
}Set;
int pot(int base,int esponente);
void stamparesti( int *resti, int n);
int main()
{
Set *ptrPDS=NULL;
int *ptr2Set=NULL;
int *resti=NULL;
int *set=NULL;
int n,m;
int i=0,j=0;
int N,Q=0;
int card=0;
printf("Inserisci il numero di elementi di S\n");
scanf("%d",&n);
m=pot(2,n);
printf("L'insieme dei sottoinsiemi di un insieme S ha %d sottoinsiemi
\n",m);
ptrPDS=(Set *)malloc(sizeof(Set)*m);
if(ptrPDS==NULL)
{
printf("Impossibile allocare spazio per l'insieme PDS: memoria
insufficiente\n");
free(ptrPDS);
pointless

exit(1);
}
set=malloc(sizeof(int)*n);
// Verifica se esiste abbastanza memoria per l'allocazione dell'insieme
if(set==NULL)
{
printf("Impossibile allocare spazio per l'insieme S: memoria
insufficiente\n");
free(set);
pointless

exit(1);
}

printf("Iserire gli elementi di S\n");
for(i=0;i<n;i++)
{
printf("\nInserire elemento %d",i);scanf("%d",set+i);
}
for(i=0;i<m;i++)
{
printf("i=%d\n",i);
resti=malloc(sizeof(int)*n);
if(resti==NULL)
{
printf("Impossibile allocare spazio per l'insieme S:
memoria insufficiente\n");
free(resti);
pointless

exit(1);
}
N=i;
//Conversione in binario del numero i
for(j=0;j<n;j++)
{
Q=N/2;
*(resti+j)=N%2;

use array notation

N=Q;
}
stamparesti(resti,n);
ptr2Set=malloc(sizeof(int));
if(ptr2Set==NULL)
{
printf("Allocazione di memoria non riuscita\n");
free(ptr2Set);
pointless

exit(1);
}
card=0;
for(j=0;j<n;j++)
{
printf("j=%d card=%d\t",j,card);
if(*(resti+j)==1)

use array notation

{
ptr2Set=realloc(ptr2Set,++card);

2nd parameter wrong - use ++card*sizeof(*ptr2Set) instead.

always store the return value in a temporary variable to check if it's NULL - upon failure, the original block remains unchanged.

that if statement looks odd - why should the decision whether to realloc the block depend on anything apart from the index being addressed, and the current size of the allocated block?

if(ptr2Set==NULL)
{
printf("Allocazione di memoria non riuscita\n");
free(ptr2Set);
pointless

exit(1);
}
*(ptr2Set+card-1)=*(set+j);

use array notation

}
}
free(resti);
(ptrPDS+i)->elementi=card;
(ptrPDS+i)->ptrSet=ptr2Set;

use array notation

printf("i=%d\telementi=%d\tptrSet=%p\n",i,card,ptr2Set);
}
// Stampa elementi sottoinsieme.
for(i=0;i<m;i++)
{
ptr2Set=(ptrPDS+i)->ptrSet;
printf("S%d={",i);
card=(ptrPDS+i)->elementi;

use array notation

if (card==0) printf("}\n");
else
{
for(j=0;j<card-1;j++) printf("%d,",*(ptr2Set+j));
printf("%d}\n",*(ptr2Set+j));

use array notation

indent/bracket consistently

}
printf("\n");

}
free(ptrPDS);
free(ptr2Set);
free(set);
return 0;
}
// Funzione per il calcolo della potenza di un numero intero n ad un
esponente
int pot(int base,int esponente)
{
int p=1;
int i=0;
while(i++<esponente)
p=p*base;
return p;
}
// Stampa dei resti
void stamparesti( int *resti, int n)
{
int j;
for(j=0;j<n;j++)
{
printf("\t%d",*(resti+j));

use array notation

}
printf("\n");
}

I use Open Suse Linux 12.2, gcc compiler 4.7.1


Francesco

Phil

 

[James Harris]

I get this strange error message

subsets.exe: malloc.c:2451: sYSMALLOc: Assertion `(old_top == (((mbinptr)

An assertion failure in malloc suggests you have previously
overwritten one or more of its internal data structures. They are
often placed between the spaces malloc/realloc gives to you and should
not be touched.

In your code I see

*(ptr2Set+card-1)=*(set+j);

Is this right? It looks like card starts out as zero so this could
refer to the memory before your allocated area that you should not
touch. This may be it - or there may be others.

James

 

[francesco]

2nd parameter wrong - use ++card*sizeof(*ptr2Set) instead.

yes, it fixed the problem. I have already fixed this sort of problems,
but now I wasn't able to see the solution

always store the return value in a temporary variable to check if it's
NULL - upon failure, the original block remains unchanged.
Ok

that if statement looks odd - why should the decision whether to realloc
the block depend on anything apart from the index being addressed, and
the current size of the allocated block?

Do you mean this uf statement ?

if(*(resti+j)==1)

I need to create sets of variable size, and the size depends upon this
test, if rest==1 I need to add an item to the set, else I don't.

{
ptr2Set=realloc(ptr2Set,++card*sizeof(int));
if(ptr2Set==NULL)
{
printf("Allocazione di memoria non riuscita\n");
free(ptr2Set);
exit(1);
}
*(ptr2Set+card-1)=*(set+j);
}

 

[francesco]

Il Sat, 22 Dec 2012 15:45:33 -0500, Eric Sosman ha scritto:

[...]
ptr2Set=realloc(ptr2Set,++card);

ptr2set = realloc(ptr2set, ++card * sizeof(int));

yes, this fixed the program, it is always a subtle error

Better,

ptr2set = realloc(ptr2set, ++card * sizeof *ptr2set);

Other improvements are possible, and there may be other
problems. Start by fixing this one, and see how far you get.

Ok, I fixed that subtle error and the program works now.

Francesco

 

[francesco]

per il resto, quando ho visto m=2^n e m usato come parametro per malloc
ed come parametro per il ciclo for: ho abbandonato...

Devo allocare un blocco di m strutture,e poi riempirle. Quindi mi serve
sia malloc con m come parametro sia ripetere il ciclo di for m volte

Francesco

 

[Ike Naar]

Sorry, this is he code

#include<stdlib.h>
#include<stdio.h>
typedef struct {
int *ptrSet;
int elementi;
}Set;
int pot(int base,int esponente);
void stamparesti( int *resti, int n);
int main()
{
Set *ptrPDS=NULL;
int *ptr2Set=NULL;
int *resti=NULL;
int *set=NULL;
int n,m;
int i=0,j=0;
int N,Q=0;
int card=0;
printf("Inserisci il numero di elementi di S\n");
scanf("%d",&n);
m=pot(2,n);
printf("L'insieme dei sottoinsiemi di un insieme S ha %d sottoinsiemi
\n",m);
ptrPDS=(Set *)malloc(sizeof(Set)*m);
if(ptrPDS==NULL)
{
printf("Impossibile allocare spazio per l'insieme PDS: memoria
insufficiente\n");
free(ptrPDS);
exit(1);
}
set=malloc(sizeof(int)*n);
// Verifica se esiste abbastanza memoria per l'allocazione dell'insieme
if(set==NULL)
{
printf("Impossibile allocare spazio per l'insieme S: memoria
insufficiente\n");
free(set);
exit(1);
}

printf("Iserire gli elementi di S\n");
for(i=0;i<n;i++)
{
printf("\nInserire elemento %d",i);scanf("%d",set+i);
}
for(i=0;i<m;i++)
{
printf("i=%d\n",i);
resti=malloc(sizeof(int)*n);
if(resti==NULL)
{
printf("Impossibile allocare spazio per l'insieme S:
memoria insufficiente\n");
free(resti);
exit(1);
}
N=i;
//Conversione in binario del numero i
for(j=0;j<n;j++)
{
Q=N/2;
*(resti+j)=N%2;
N=Q;
}
stamparesti(resti,n);
ptr2Set=malloc(sizeof(int));
if(ptr2Set==NULL)
{
printf("Allocazione di memoria non riuscita\n");
free(ptr2Set);
exit(1);
}
card=0;
for(j=0;j<n;j++)
{
printf("j=%d card=%d\t",j,card);
if(*(resti+j)==1)
{
ptr2Set=realloc(ptr2Set,++card);
if(ptr2Set==NULL)
{
printf("Allocazione di memoria non riuscita\n");
free(ptr2Set);
exit(1);
}
*(ptr2Set+card-1)=*(set+j);
}
}
free(resti);
(ptrPDS+i)->elementi=card;
(ptrPDS+i)->ptrSet=ptr2Set;
printf("i=%d\telementi=%d\tptrSet=%p\n",i,card,ptr2Set);
}
// Stampa elementi sottoinsieme.
for(i=0;i<m;i++)
{
ptr2Set=(ptrPDS+i)->ptrSet;
printf("S%d={",i);
card=(ptrPDS+i)->elementi;
if (card==0) printf("}\n");
else
{
for(j=0;j<card-1;j++) printf("%d,",*(ptr2Set+j));
printf("%d}\n",*(ptr2Set+j));
}
printf("\n");

}
free(ptrPDS);
free(ptr2Set);

There is a malloc/free mismatch here.
You allocate n regions of memory, using ptr2Set=malloc(/*...*/) in a loop,
but only one of them is freed at the end of the program.

 

[francesco]

Il Sun, 23 Dec 2012 17:12:01 -0500, pete ha scritto:

After thinking more,
I think that it makes more sense to allocate (ptr2Set) prior to the
loop,
and to then free it after the loop.

As I did it

And it also makes more sense to allocate (resti) prior to the loop, and
to then free it after the loop.

puts("Inserisci il numero di elementi di S"); scanf("%d", &n);
m = pot(2, n);
printf("L'insieme dei sottoinsiemi di un insieme S ha %d"
" sottoinsiemi\n", m);
ptrPDS = malloc(m * sizeof *ptrPDS);
set = malloc(n * sizeof *set);
resti = malloc(n * sizeof *resti);

resti is an array of int values, dinamically created

ptr2Set = malloc(sizeof *ptr2Set);

ptr2Set is an array of int values, dinamically created

/*
** Verifica se esiste abbastanza ** memoria per l'allocazione
dell'insieme */
if (ptrPDS == NULL || set == NULL
|| resti == NULL || ptr2Set == NULL)
{
free(resti);
free(set);
free(ptrPDS);
free(ptr2Set);
puts("Allocazione di memoria non riuscita"); exit(EXIT_FAILURE);
}
puts("Iserire gli elementi di S");
for (i = 0; n > i; ++i) {
printf("\nInserire elemento %d ", i);
fflush(stdout);
scanf("%d", set + i);
}
for (i = 0; m > i; ++i) {
printf("i=%d ", i);
N = i;
/*
** Conversione in binario del numero i */
for (j = 0; n > j; ++j) {
Q = N / 2;
resti[j] = N % 2;
N = Q;
}
stamparesti(resti, n);
card = 0;
for (j = 0; n > j; ++j) {
printf("j=%d card=%d\n", j, card);
if (resti[j] == 1) {
void *temp;

temp = realloc(ptr2Set, (card + 1) * sizeof *ptr2Set);
if (temp == NULL) {
free(ptr2Set);
free(resti);
free(set);
free(ptrPDS);
puts("Allocazione di memoria non riuscita");
exit(EXIT_FAILURE);
}
ptr2Set = temp;
ptr2Set[card++] = set[j];
}
}
ptrPDS.elementi = card;
ptrPDS.ptrSet = ptr2Set;
printf("elementi=%d ptrSet=%p\n\n\n\n", card, ptr2Set);
}
free(ptr2Set);
free(resti);
free(set);

Thak you for your advices.

Francesco

 

[Ralph Spitzner]

Phil Carmody wrote:
[...]

pointless

Apart from it being pointless he's actually trying to free a
NULL pointer

-rasp

 

[Richard Damon]

Phil Carmody wrote:
[...]

pointless

Apart from it being pointless he's actually trying to free a
NULL pointer

-rasp

It is perfectly legal to free a null pointer. The free() function has
defined behavior in this case, it does nothing.

The fact that he KNOWS it is a null pointer, is what makes the call
pointless, it just becomes a waste of a few CPU cycles.

 

[James Kuyper]

Phil Carmody wrote:
[...]

pointless

Apart from it being pointless he's actually trying to free a
NULL pointer

"NULL" is the name of a standard macro that's required to expand into a
null pointer constant - due to one of the quirks of C jargon, a null
pointer constant is not necessarily a pointer, null or otherwise; it can
be an integer. He's calling free(set), not free(NULL). In the comparison
between set and NULL, NULL gets converted to a null pointer of the same
type as "set"; if that branch has been entered, they compared equal,
which means that "set" is also a null pointer. The word you should have
used was "null", not "NULL".

 

[James Harris]

card is incremented as a function call argument
prior to that line.

Sure, you're right. I didn't want to spend the time to understand the
OP's specific code so I made that part of my post a question rather
than a statement. It was meant to illustrate the potential issue
rather than be the specific cause. The main point of the post was the
part about corrupting malloc/realloc data structures.

I don't increment arguments in function calls,
because I've been advised against it
as a matter of style.

Interesting. I can't see a problem with it.

James

 

[Phil Carmody]

Phil Carmody wrote:
[...]

pointless

Apart from it being pointless he's actually trying to free a
NULL pointer

No, that *is* the pointless bit. It's nothing more than pointless though.
(Apart from it also being a warning sign about what to expect elsewhere
in the code.)

Phil

 

[army1987]

(BTW the layout of your code could be improved!)

I suspect he's using tab characters to indent, but something along the
line (his newsreader, his news server, your news server, your newsreader)
strips them away.