Realloc destroys?

[ifmusic]

I used to think that i knew to program in C but this problem is making
me thing otherwise.
i'm trying to do something trivial, i suppose.
i have this struct:

typedef struct{
int socket;
char ip[16];
}peers;

in a main() i malloc this way:
Peers=malloc(si zeof(peers));
Then, my program would eventually want to save more "peers" so
i said, why dont i Realloc this thing x2 x3 x4 x5 and so on.. as
needed. So i created this function:

peers* ingresaripsock( peers* lista,int sock, char ip[16],int *tm)
{
int offset= (*tm)++;

if (offset>0) lista = realloc(lista,o ffset * sizeof(peers)+1 );

strcpy((lista + offset)->ip, ip);
(lista + offset)-> socket=sock;

return lista;
}

i print the results with:

void imprimirpeers(p eers* lista, int tm){
int i=0;

for(i=0;i<tm;i+ +){
printf("Ip: %s - Sock: %d\n",(lista + i) ->ip , (lista + i)
->socket);
}
}
but when i printf the Results, it's all weird data. I believe the
problem is around the Realloc becuase i tried this code but instead of
using realloc i malloc'd from the first time with space for like 20
positions (commented the realloc part in the function) and it worked
just fine. But i want to use what i Really need, dont want to do malloc
( 20000000) and use a couple of bytes...
Please i really need some help-

[Martin Ambuhl]

if*****@gmail.c om wrote:

if (offset>0) lista = realloc(lista,o ffset * sizeof(peers)+1 );

This is a severe mistake. Never use the form
ptr = realloc(ptr, size);
Instead have the results of the realloc() assigned to a temporary
variable to give you at least the option of what to do if realloc fails.

[ifmusic]

yes, after writing the post, i read some of that, i'm switchin to a
pointer to pointer data structure. hope it works that way.
Thanks.

[Christian Bau]

In article <11************ **********@o13g 2000cwo.googleg roups.com>,
if*****@gmail.c om wrote:

I used to think that i knew to program in C but this problem is making
me thing otherwise.
i'm trying to do something trivial, i suppose.
i have this struct:

typedef struct{
int socket;
char ip[16];
}peers;

in a main() i malloc this way:
Peers=malloc(si zeof(peers));
Then, my program would eventually want to save more "peers" so
i said, why dont i Realloc this thing x2 x3 x4 x5 and so on.. as
needed. So i created this function:

peers* ingresaripsock( peers* lista,int sock, char ip[16],int *tm)
{
int offset= (*tm)++;

if (offset>0) lista = realloc(lista,o ffset * sizeof(peers)+1 );

Your calculation how many bytes are needed looks interesting.

[Barry Schwarz]

On 10 Oct 2005 14:06:47 -0700, if*****@gmail.c om wrote:

I used to think that i knew to program in C but this problem is making
me thing otherwise.
i'm trying to do something trivial, i suppose.
i have this struct:

typedef struct{
int socket;
char ip[16];
}peers;

in a main() i malloc this way:
Peers=malloc(s izeof(peers));
Then, my program would eventually want to save more "peers" so
i said, why dont i Realloc this thing x2 x3 x4 x5 and so on.. as
needed. So i created this function:

peers* ingresaripsock( peers* lista,int sock, char ip[16],int *tm)
Is *tm a count of how may structures your currently have space for?
{
int offset= (*tm)++;
offset is the original value of *tm.

if (offset>0) lista = realloc(lista,o ffset * sizeof(peers)+1 );
What did you think the +1 does. What you have done, if realloc
succeeds, is allocate space for the same number of structures plus one
more byte. You did not allocate space for an extra struct. Did you
really mean
... = realloc(lista, (offset+1) * sizeof(peers));

strcpy((list a + offset)->ip, ip);
As it stands now, this invokes undefined behavior. lista points to an
allocated area capable of holding offset structures. The structures
are numbered 0, 1, ..., offset-1. You are now writing beyond the end
of your allocated area.
(lista + offset)-> socket=sock;

return lista;
}

i print the results with:

void imprimirpeers(p eers* lista, int tm){
int i=0;

for(i=0;i<tm;i ++){
printf("Ip: %s - Sock: %d\n",(lista + i) ->ip , (lista + i)
->socket);
}
}
but when i printf the Results, it's all weird data. I believe the
problem is around the Realloc becuase i tried this code but instead of
using realloc i malloc'd from the first time with space for like 20
positions (commented the realloc part in the function) and it worked
just fine. But i want to use what i Really need, dont want to do malloc
( 20000000) and use a couple of bytes...
Please i really need some help-

<<Remove the del for email>>

[ifmusic]

Thank you all for all the feedback,
now i have a pointer to pointer structure.

typedef struct{
int socket;
char id[16];
}reqs;

reqs** ingresaridsock( reqs** lista,int sock, char id[16],int *tm){
int i;
reqs* aux;
reqs **temp;
int offset= (*tm)++;
aux = malloc(sizeof(r eqs));
if (offset > 0 ){
if ((temp = realloc(lista, (offset+1) * sizeof(*lista)) )==NULL)
exit(1);
lista=temp;}
strcpy(aux->id, id);
aux->socket= sock;
lista[offset]= aux;
return lista;

Now, it seems to work just fine. BUT!, i add 1,2,3,4 and on the fifth
item,
i get Segmentation Fault! Knowing that i'm not freeing memory as i
should
shouldn't it be possible to store more than 4 miserable items without
freeing?!.

thanks again.

Barry Schwarz ha escrito:

On 10 Oct 2005 14:06:47 -0700, if*****@gmail.c om wrote:

I used to think that i knew to program in C but this problem is making
me thing otherwise.
i'm trying to do something trivial, i suppose.
i have this struct:

typedef struct{
int socket;
char ip[16];
}peers;

in a main() i malloc this way:
Peers=malloc(s izeof(peers));
Then, my program would eventually want to save more "peers" so
i said, why dont i Realloc this thing x2 x3 x4 x5 and so on.. as
needed. So i created this function:

peers* ingresaripsock( peers* lista,int sock, char ip[16],int *tm)

Is *tm a count of how may structures your currently have space for?

{
int offset= (*tm)++;

offset is the original value of *tm.

if (offset>0) lista = realloc(lista,o ffset * sizeof(peers)+1 );

What did you think the +1 does. What you have done, if realloc
succeeds, is allocate space for the same number of structures plus one
more byte. You did not allocate space for an extra struct. Did you
really mean
... = realloc(lista, (offset+1) * sizeof(peers));

strcpy((list a + offset)->ip, ip);

As it stands now, this invokes undefined behavior. lista points to an
allocated area capable of holding offset structures. The structures
are numbered 0, 1, ..., offset-1. You are now writing beyond the end
of your allocated area.

(lista + offset)-> socket=sock;

return lista;
}

i print the results with:

void imprimirpeers(p eers* lista, int tm){
int i=0;

for(i=0;i<tm;i ++){
printf("Ip: %s - Sock: %d\n",(lista + i) ->ip , (lista + i)
->socket);
}
}
but when i printf the Results, it's all weird data. I believe the
problem is around the Realloc becuase i tried this code but instead of
using realloc i malloc'd from the first time with space for like 20
positions (commented the realloc part in the function) and it worked
just fine. But i want to use what i Really need, dont want to do malloc
( 20000000) and use a couple of bytes...
Please i really need some help-

<<Remove the del for email>>

[ifmusic]

Here is something new,
if the first time i malloc(15*sizeo f(*Reqs)) it works fine. So i
commented the Realloc part in the function i tried it. But Something i
did not expect ,happened, it didn't just stored 15 items but it seemed
to be "endless", i stored tons of items as if there was no need for a
Realloc. WHY?!.

ifmu...@gmail.c om ha escrito:

Thank you all for all the feedback,
now i have a pointer to pointer structure.

typedef struct{
int socket;
char id[16];
}reqs;

reqs** ingresaridsock( reqs** lista,int sock, char id[16],int *tm){
int i;
reqs* aux;
reqs **temp;
int offset= (*tm)++;
aux = malloc(sizeof(r eqs));
if (offset > 0 ){
if ((temp = realloc(lista, (offset+1) * sizeof(*lista)) )==NULL)
exit(1);
lista=temp;}
strcpy(aux->id, id);
aux->socket= sock;
lista[offset]= aux;
return lista;

Now, it seems to work just fine. BUT!, i add 1,2,3,4 and on the fifth
item,
i get Segmentation Fault! Knowing that i'm not freeing memory as i
should
shouldn't it be possible to store more than 4 miserable items without
freeing?!.

thanks again.

Barry Schwarz ha escrito:

On 10 Oct 2005 14:06:47 -0700, if*****@gmail.c om wrote:

I used to think that i knew to program in C but this problem is making
me thing otherwise.
i'm trying to do something trivial, i suppose.
i have this struct:

typedef struct{
int socket;
char ip[16];
}peers;

in a main() i malloc this way:
Peers=malloc(s izeof(peers));
Then, my program would eventually want to save more "peers" so
i said, why dont i Realloc this thing x2 x3 x4 x5 and so on.. as
needed. So i created this function:

peers* ingresaripsock( peers* lista,int sock, char ip[16],int *tm)

Is *tm a count of how may structures your currently have space for?

{
int offset= (*tm)++;

offset is the original value of *tm.

if (offset>0) lista = realloc(lista,o ffset * sizeof(peers)+1 );

What did you think the +1 does. What you have done, if realloc
succeeds, is allocate space for the same number of structures plus one
more byte. You did not allocate space for an extra struct. Did you
really mean
... = realloc(lista, (offset+1) * sizeof(peers));

strcpy((list a + offset)->ip, ip);

As it stands now, this invokes undefined behavior. lista points to an
allocated area capable of holding offset structures. The structures
are numbered 0, 1, ..., offset-1. You are now writing beyond the end
of your allocated area.

(lista + offset)-> socket=sock;

return lista;
}

i print the results with:

void imprimirpeers(p eers* lista, int tm){
int i=0;

for(i=0;i<tm;i ++){
printf("Ip: %s - Sock: %d\n",(lista + i) ->ip , (lista + i)
->socket);
}
}
but when i printf the Results, it's all weird data. I believe the
problem is around the Realloc becuase i tried this code but instead of
using realloc i malloc'd from the first time with space for like 20
positions (commented the realloc part in the function) and it worked
just fine. But i want to use what i Really need, dont want to do malloc
( 20000000) and use a couple of bytes...
Please i really need some help-

<<Remove the del for email>>

[Old Wolf]

if*****@gmail.c om wrote:

typedef struct{
int socket;
char id[16];
}reqs;

reqs** ingresaridsock( reqs** lista,int sock, char id[16],int *tm){
int i;
reqs* aux;
reqs **temp;
int offset= (*tm)++;
aux = malloc(sizeof(r eqs));
if (offset > 0 ){
if ((temp = realloc(lista, (offset+1) * sizeof(*lista)) )==NULL)
exit(1);
lista=temp;}
You never allocate anything when *tm was 0.
If lista were NULL (or an array of size 0), then you would
cause undefined behaviour.
strcpy(aux->id, id);
aux->socket= sock;
lista[offset]= aux;
return lista;

Now, it seems to work just fine. BUT!, i add 1,2,3,4 and on the
fifth item, i get Segmentation Fault!

If the above was not the problem, then perhaps you have a buffer
overflow in the strcpy, or some other heap corruption. Can you
post a complete, compilable program that demonstrates the problem?

BTW, please don't top-post ( http://en.wikipedia.org/wiki/Top-posting )

[ifmusic]

There's no problem about the tm being 0.

the thing with posting the whole thing is that i don't know how you're
gonna test it. I'm testing it with 3 vmwares as clients and 1 vmware as
server which is storing the info.

Again, something that's still bugging me is the "endless" list i'm
getting...

if you want i can mail you the code.

Thanks for the help-

[Barry Schwarz]

On 10 Oct 2005 18:11:39 -0700, if*****@gmail.c om wrote:

Thank you all for all the feedback,
now i have a pointer to pointer structure.

typedef struct{
int socket;
char id[16];
}reqs;

reqs** ingresaridsock( reqs** lista,int sock, char id[16],int *tm){
int i;
reqs* aux;
reqs **temp;
int offset= (*tm)++;
aux = malloc(sizeof(r eqs));
if (offset > 0 ){
if ((temp = realloc(lista, (offset+1) * sizeof(*lista)) )==NULL)
exit(1);
lista=temp;}
strcpy(aux->id, id);
aux->socket= sock;
lista[offset]= aux;
return lista;

Now, it seems to work just fine. BUT!, i add 1,2,3,4 and on the fifth
item,
i get Segmentation Fault! Knowing that i'm not freeing memory as i
should
shouldn't it be possible to store more than 4 miserable items without
freeing?!.

On which statement does the seg fault occur?

How are you calling this function? Show us main.
<<Remove the del for email>>