Re: problem with malloc/realloc. Pls help.
Thanks a lot, Igor Mark. i was able to rectify the
code to fix the problem. Now it works. (i had to use a
pointer to a pointer to int, rather than just a
pointer to int in the subroutine)
thanks again.
o.
--- Igor Peshansky [EMAIL PROTECTED] wrote:
On Mon, 21 Aug 2006, Omololu wrote:
Hi,
i have the following code. it compiles with gcc
in Cygwin but the
contents of the array ifitQ that I get after the
call to the subroutine
readCharges2 is gibberish.
This is expected behavior. Read on.
The code compiles with gcc under Linux and it runs
correctly. it also
compiles and runs correctly with windows visual
studio. Pls help. The
resuls i get with Cygwin is:
isumNatms = 5
rrr 13
rrr 14
rrr 15
rrr 16
*** 1628693268
*** 1628693268
*** 16
*** 1034
instead of:
isumNatms = 5
rrr 13
rrr 14
rrr 15
rrr 16
*** 13
*** 14
*** 15
*** 16
the code is:
Ouch. Indentation issues aside, you have a bug in
this program.
#include stdio.h
#include stdlib.h
void readCharges2(int *, int *, int *);
int main()
{
static int *ifitQ;
int *ipUniqAtms, *ipindexToFit;
int j;
int x,y;
ipUniqAtms =x;
ipindexToFit=y;
ifitQ = (int *)
malloc(sizeof(int));
if(ifitQ==NULL){printf(Unable to allocate
matrix ifitQ\n);
exit(EXIT_FAILURE);}
readCharges2(ifitQ,ipUniqAtms,ipindexToFit);
Note that ifitQ is passed *by value*, and any
changes you make to it
inside readCharges2() will be lost when you come
back to main. So, you
realloc it inside readCharges2(), and store values
in the new array, but
in main(), you print the values in the *old* array
(which are, as you
said, gibberish, as the memory has been released to
the system).
for(j=0; j *ipUniqAtms ; j++)
{
printf(*** %d\n,ifitQ[j]);
}
return 0;
}
void readCharges2(int *ifitQ, int * ipUniqAtms,
int * ipindexToFit)
{
int j, isumNatms=0;
isumNatms=5;
printf(isumNatms = %d \n,isumNatms);
ifitQ = (int *)
realloc(ifitQ,isumNatms*sizeof(int));
if(ifitQ==NULL){printf(Unable to allocate
matrix ifitQ\n);
exit(EXIT_FAILURE);}
ifitQ[0]=13;
ifitQ[1]=14;
ifitQ[2]=15;
ifitQ[3]=16;
*ipUniqAtms = 4;
*ipindexToFit = 3;
for(j=0; j *ipUniqAtms ; j++)
{
printf(rrr %d\n,ifitQ[j]);
}
}
The reason it probably worked on Linux is because in
Linux, realloc will
try hard to keep the array at the same address if it
can simply bump the
size of the pointer. Cygwin's realloc doesn't.
HTH,
Igor
--
http://cs.nyu.edu/~pechtcha/
|\ _,,,---,,_ [EMAIL PROTECTED] |
[EMAIL PROTECTED]
ZZZzz /,`.-'`'-. ;-;;,_ Igor Peshansky, Ph.D.
(name changed!)
|,4- ) )-,_. ,\ ( `'-' old name: Igor
Pechtchanski
'---''(_/--' `-'\_) fL a.k.a
JaguaR-R-R-r-r-r-.-.-. Meow!
Las! je suis sot... -Mais non, tu ne l'es pas,
puisque tu t'en rends compte.
But no -- you are no fool; you call yourself a
fool, there's proof enough in
that! -- Rostand, Cyrano de Bergerac
* SEEK GOD! ***
--
Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
Problem reports: http://cygwin.com/problems.html
Documentation: http://cygwin.com/docs.html
FAQ: http://cygwin.com/faq/
Re: problem with malloc/realloc. Pls help.
On Mon, 21 Aug 2006, Omololu wrote:
Hi,
i have the following code. it compiles with gcc in Cygwin but the
contents of the array ifitQ that I get after the call to the subroutine
readCharges2 is gibberish.
This is expected behavior. Read on.
The code compiles with gcc under Linux and it runs correctly. it also
compiles and runs correctly with windows visual studio. Pls help. The
resuls i get with Cygwin is:
isumNatms = 5
rrr 13
rrr 14
rrr 15
rrr 16
*** 1628693268
*** 1628693268
*** 16
*** 1034
instead of:
isumNatms = 5
rrr 13
rrr 14
rrr 15
rrr 16
*** 13
*** 14
*** 15
*** 16
the code is:
Ouch. Indentation issues aside, you have a bug in this program.
#include stdio.h
#include stdlib.h
void readCharges2(int *, int *, int *);
int main()
{
static int *ifitQ;
int *ipUniqAtms, *ipindexToFit;
int j;
int x,y;
ipUniqAtms =x;
ipindexToFit=y;
ifitQ = (int *) malloc(sizeof(int));
if(ifitQ==NULL){printf(Unable to allocate matrix ifitQ\n);
exit(EXIT_FAILURE);}
readCharges2(ifitQ,ipUniqAtms,ipindexToFit);
Note that ifitQ is passed *by value*, and any changes you make to it
inside readCharges2() will be lost when you come back to main. So, you
realloc it inside readCharges2(), and store values in the new array, but
in main(), you print the values in the *old* array (which are, as you
said, gibberish, as the memory has been released to the system).
for(j=0; j *ipUniqAtms ; j++)
{
printf(*** %d\n,ifitQ[j]);
}
return 0;
}
void readCharges2(int *ifitQ, int * ipUniqAtms, int * ipindexToFit)
{
int j, isumNatms=0;
isumNatms=5;
printf(isumNatms = %d \n,isumNatms);
ifitQ = (int *) realloc(ifitQ,isumNatms*sizeof(int));
if(ifitQ==NULL){printf(Unable to allocate matrix ifitQ\n);
exit(EXIT_FAILURE);}
ifitQ[0]=13;
ifitQ[1]=14;
ifitQ[2]=15;
ifitQ[3]=16;
*ipUniqAtms = 4;
*ipindexToFit = 3;
for(j=0; j *ipUniqAtms ; j++)
{
printf(rrr %d\n,ifitQ[j]);
}
}
The reason it probably worked on Linux is because in Linux, realloc will
try hard to keep the array at the same address if it can simply bump the
size of the pointer. Cygwin's realloc doesn't.
HTH,
Igor
--
http://cs.nyu.edu/~pechtcha/
|\ _,,,---,,_[EMAIL PROTECTED] | [EMAIL PROTECTED]
ZZZzz /,`.-'`'-. ;-;;,_Igor Peshansky, Ph.D. (name changed!)
|,4- ) )-,_. ,\ ( `'-' old name: Igor Pechtchanski
'---''(_/--' `-'\_) fL a.k.a JaguaR-R-R-r-r-r-.-.-. Meow!
Las! je suis sot... -Mais non, tu ne l'es pas, puisque tu t'en rends compte.
But no -- you are no fool; you call yourself a fool, there's proof enough in
that! -- Rostand, Cyrano de Bergerac
--
Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
Problem reports: http://cygwin.com/problems.html
Documentation: http://cygwin.com/docs.html
FAQ: http://cygwin.com/faq/
Re: problem with malloc/realloc. Pls help.
On Mon, 21 Aug 2006, Igor Peshansky wrote:
On Mon, 21 Aug 2006, Omololu wrote:
Hi,
i have the following code. it compiles with gcc in Cygwin but the
contents of the array ifitQ that I get after the call to the subroutine
readCharges2 is gibberish.
This is expected behavior. Read on.
The code compiles with gcc under Linux and it runs correctly. it also
compiles and runs correctly with windows visual studio. Pls help. The
resuls i get with Cygwin is:
isumNatms = 5
rrr 13
rrr 14
rrr 15
rrr 16
*** 1628693268
*** 1628693268
*** 16
*** 1034
instead of:
isumNatms = 5
rrr 13
rrr 14
rrr 15
rrr 16
*** 13
*** 14
*** 15
*** 16
the code is:
Ouch. Indentation issues aside, you have a bug in this program.
#include stdio.h
#include stdlib.h
void readCharges2(int *, int *, int *);
int main()
{
static int *ifitQ;
int *ipUniqAtms, *ipindexToFit;
int j;
int x,y;
ipUniqAtms =x;
ipindexToFit=y;
ifitQ = (int *) malloc(sizeof(int));
if(ifitQ==NULL){printf(Unable to allocate matrix ifitQ\n);
exit(EXIT_FAILURE);}
readCharges2(ifitQ,ipUniqAtms,ipindexToFit);
Note that ifitQ is passed *by value*, and any changes you make to it
inside readCharges2() will be lost when you come back to main. So, you
realloc it inside readCharges2(), and store values in the new array, but
in main(), you print the values in the *old* array (which are, as you
said, gibberish, as the memory has been released to the system).
for(j=0; j *ipUniqAtms ; j++)
{
printf(*** %d\n,ifitQ[j]);
}
return 0;
}
void readCharges2(int *ifitQ, int * ipUniqAtms, int * ipindexToFit)
{
int j, isumNatms=0;
isumNatms=5;
printf(isumNatms = %d \n,isumNatms);
ifitQ = (int *) realloc(ifitQ,isumNatms*sizeof(int));
if(ifitQ==NULL){printf(Unable to allocate matrix ifitQ\n);
exit(EXIT_FAILURE);}
ifitQ[0]=13;
ifitQ[1]=14;
ifitQ[2]=15;
ifitQ[3]=16;
*ipUniqAtms = 4;
*ipindexToFit = 3;
for(j=0; j *ipUniqAtms ; j++)
{
printf(rrr %d\n,ifitQ[j]);
}
}
The reason it probably worked on Linux is because in Linux, realloc will
try hard to keep the array at the same address if it can simply bump the
size of the pointer. Cygwin's realloc doesn't.
s/pointer/memory block/. Sorry for the typo.
Igor
--
http://cs.nyu.edu/~pechtcha/
|\ _,,,---,,_[EMAIL PROTECTED] | [EMAIL PROTECTED]
ZZZzz /,`.-'`'-. ;-;;,_Igor Peshansky, Ph.D. (name changed!)
|,4- ) )-,_. ,\ ( `'-' old name: Igor Pechtchanski
'---''(_/--' `-'\_) fL a.k.a JaguaR-R-R-r-r-r-.-.-. Meow!
Las! je suis sot... -Mais non, tu ne l'es pas, puisque tu t'en rends compte.
But no -- you are no fool; you call yourself a fool, there's proof enough in
that! -- Rostand, Cyrano de Bergerac
--
Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
Problem reports: http://cygwin.com/problems.html
Documentation: http://cygwin.com/docs.html
FAQ: http://cygwin.com/faq/
Re: problem with malloc/realloc. Pls help.
On 8/21/06, Omololu wrote: Hi, i have the following code. it compiles with gcc in Cygwin but the contents of the array ifitQ that I get after the call to the subroutine readCharges2 is gibberish. looks like a passing by reference problem. if you add debug to look at the address of ifitQ at all stages, you'll notice that the copy pointer in readCharges2 gets changed, but that isn't the same pointer as in the calling block. see section 2.17 of http://www.lysator.liu.se/c/c-faq/c-2.html i don't understand how linux is getting it right tbh. -- Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple Problem reports: http://cygwin.com/problems.html Documentation: http://cygwin.com/docs.html FAQ: http://cygwin.com/faq/
