Re: error allocating memory with realloc(). how can i increase max_allowed in the system?

2008-08-20 Thread Derek Taylor 
On Tue, 12 Aug 2008, Jordi Moles Blanco wrote:
Hi,

i'm running a FreeBSD 7.0 amd64 machine and struggling with some C code 
i'm writing.

In addition to the other comments already given, I think that it might
be useful for your learning experience to have some additional comments.

I've had some trouble with this home-made script as it keeps crashing 
while launching a realloc() call.

I narrowed down the problem and here i'm sending you a short example of 
code that crashes:

*
#include stdio.h
#include stdlib.h

int main()
{

int midataula;

midataula = 3000;

char *missatge = (char *)malloc(midataula * sizeof(char));

You should not cast the return value of malloc. [1]

missatge[0]='h';
missatge[1]='o';
missatge[2]='l';
missatge[3]='a';

Recall that malloc() makes no promises about the contents of the memory
allocated.  I recommend, in the current style, adding:
 missatge[4]='\0';

printf(\n\ntaula1: %s,missatge);

int voltes;
voltes = 0;

Traditionally in C, all variable declarations appear at the beginning of
the local scope.  Declaring new variables mid-scope is valid in certain
off-shoots of C and may be acceptable in newer dialects/standards of the
language, but the majority of C programmers might make certain
assumptions about your code following older traditions.

This certainly is not too egregious, but while I was here, I thought I'd
mention it. 

while(voltes4)
{
midataula = midataula+500;
realloc(missatge, midataula * sizeof(char));
voltes++;
}


printf(\n\ntaula2: %s,missatge);
}
*


this is a full working you can compile on your machine.

Like this... i get Segmentation fault (core dumped)

but if instead of while(voltes4) i use while(voltes3)

the script works fine with this output:

**
taula1: hola

taula2: hola
**

so... i guess there must be a limit in the system somewhere.

I've tried to reset all variables that i've seen in the sysctl -a list 
refering to malloc, memory, mem, and so on... but so far i haven't fixed 
the problem.

i'm running this script as root and in the /etc/login.conf file there's 
only the default group with the unlimited values.
A part from that, if i perform a limit call, i get this:

*

# limit
cputime  unlimited
filesize unlimited
datasize 33554432 kbytes
stacksize524288 kbytes
coredumpsize unlimited
memoryuseunlimited
vmemoryuse   unlimited
descriptors  45000
memorylocked unlimited
maxproc  22500
sbsize   unlimited

*

i've tried to resize datasize and stacksize, but the system won't let me 
do so.

any idea how to solve this?

thanks.


Good luck with your programming and systems work!

-Derek.

[1] http://c-faq.com/malloc/mallocnocast.html
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error allocating memory with realloc(). how can i increase max_allowed in the system?

2008-08-12 Thread Jordi Moles Blanco 

Hi,

i'm running a FreeBSD 7.0 amd64 machine and struggling with some C code 
i'm writing.


I've had some trouble with this home-made script as it keeps crashing 
while launching a realloc() call.


I narrowed down the problem and here i'm sending you a short example of 
code that crashes:


*
#include stdio.h
#include stdlib.h

int main()
{

   int midataula;

   midataula = 3000;

   char *missatge = (char *)malloc(midataula * sizeof(char));

   missatge[0]='h';
   missatge[1]='o';
   missatge[2]='l';
   missatge[3]='a';

   printf(\n\ntaula1: %s,missatge);

   int voltes;
   voltes = 0;

   while(voltes4)
   {
   midataula = midataula+500;
   realloc(missatge, midataula * sizeof(char));
   voltes++;
   }


   printf(\n\ntaula2: %s,missatge);
}
*


this is a full working you can compile on your machine.

Like this... i get Segmentation fault (core dumped)

but if instead of while(voltes4) i use while(voltes3)

the script works fine with this output:

**
taula1: hola

taula2: hola
**

so... i guess there must be a limit in the system somewhere.

I've tried to reset all variables that i've seen in the sysctl -a list 
refering to malloc, memory, mem, and so on... but so far i haven't fixed 
the problem.


i'm running this script as root and in the /etc/login.conf file there's 
only the default group with the unlimited values.

A part from that, if i perform a limit call, i get this:

*

# limit
cputime  unlimited
filesize unlimited
datasize 33554432 kbytes
stacksize524288 kbytes
coredumpsize unlimited
memoryuseunlimited
vmemoryuse   unlimited
descriptors  45000
memorylocked unlimited
maxproc  22500
sbsize   unlimited

*

i've tried to resize datasize and stacksize, but the system won't let me 
do so.


any idea how to solve this?

thanks.

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Re: error allocating memory with realloc(). how can i increase max_allowed in the system?

2008-08-12 Thread Giorgos Keramidas 
On Tue, 12 Aug 2008 17:02:43 +0200, Jordi Moles Blanco [EMAIL PROTECTED] 
wrote:
 Hi,

 i'm running a FreeBSD 7.0 amd64 machine and struggling with some C
 code i'm writing.

 I've had some trouble with this home-made script as it keeps crashing
 while launching a realloc() call.

 I narrowed down the problem and here i'm sending you a short example of
 code that crashes:

 *
 #include stdio.h
 #include stdlib.h

 int main()
 {

int midataula;

midataula = 3000;

char *missatge = (char *)malloc(midataula * sizeof(char));

missatge[0]='h';
missatge[1]='o';
missatge[2]='l';
missatge[3]='a';

printf(\n\ntaula1: %s,missatge);

int voltes;
voltes = 0;

while(voltes4)
{
midataula = midataula+500;
realloc(missatge, midataula * sizeof(char));
voltes++;
}

There's your problem.  realloc() works fine, but it *returns* the new
pointer; it does _not_ modify missatge in place.

The program should work fine if you use size_t for midataula (it is the
'size' of an array, which may not necessarily fit in an 'int'), and if
you use realloc() correctly, as in:

#include stdlib.h
#include err.h

size_t midataula;
char *missatge;

/*
 * DON'T cast the result of malloc().  It may 'hide' the bug of
 * a missing stdlib.h include, and cause troubles when
 * malloc() is implicitly defined by the compiler as:
 *
 *int malloc(...);
 *
 * On a 64-bit machine converting a 64-bit pointer to `int' will
 * lose the high-order 32 bits of the address, and you will try
 * to access unexpected memory areas.
 */
midataula = 3000;
missatge = malloc(midataula * sizeof(*missatge));
if (missatge == NULL)
err(1, malloc);

Then when you use realloc() keep both midataula and missatge in
temporary copies until you are sure that realloc() worked:

while (voltes  4) {
char *tmp;
size_t newsize;

newsize = midataula + 500;
tmp = realloc(missatge, newsize * sizeof(*missatge));
if (tmp == NULL)
err(1, realloc);

/*
 * Now that you know the resize has succeeded, update
 * midataula and missatge.  realloc() is allowed to
 * relocate missatge.  See the following note in its
 * manpage:
 *
 *   Note that realloc() and reallocf() may move the
 *   memory allocation, resulting in a different return
 *   value than ptr.
 */
midataula = newsize;
missatge = tmp;
}

Right now you are calling realloc() as:

realloc(missatge, newsize * sizeof(*missatge));

and throwing away the resulting pointer.  The first time that realloc()
discovers that the `resized' vector cannot fit in its original location,
it relocates the array, and returns the new location.  You throw away
that location and your next iteration through the loop tries to access
an invalid (already freed) memory region.

That's what causes your segmentation fault.

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Re: error allocating memory with realloc(). how can i increase max_allowed in the system? [solved]

2008-08-12 Thread Jordi Moles Blanco 

Hello,

thank you very much for your time and help, i had completely 
misunderstood how realloc() works.


i though i was able to write some C code but now i feel a complete 
newbie, hehehe.


anyway... that made everything clear to me and now my script is working 
like a charm.


thanks for everything

En/na Giorgos Keramidas ha escrit:

On Tue, 12 Aug 2008 17:02:43 +0200, Jordi Moles Blanco [EMAIL PROTECTED] 
wrote:
  

Hi,

i'm running a FreeBSD 7.0 amd64 machine and struggling with some C
code i'm writing.

I've had some trouble with this home-made script as it keeps crashing
while launching a realloc() call.

I narrowed down the problem and here i'm sending you a short example of
code that crashes:

*
#include stdio.h
#include stdlib.h

int main()
{

   int midataula;

   midataula = 3000;

   char *missatge = (char *)malloc(midataula * sizeof(char));

   missatge[0]='h';
   missatge[1]='o';
   missatge[2]='l';
   missatge[3]='a';

   printf(\n\ntaula1: %s,missatge);

   int voltes;
   voltes = 0;

   while(voltes4)
   {
   midataula = midataula+500;
   realloc(missatge, midataula * sizeof(char));
   voltes++;
   }



There's your problem.  realloc() works fine, but it *returns* the new
pointer; it does _not_ modify missatge in place.

The program should work fine if you use size_t for midataula (it is the
'size' of an array, which may not necessarily fit in an 'int'), and if
you use realloc() correctly, as in:

#include stdlib.h
#include err.h

size_t midataula;
char *missatge;

/*
 * DON'T cast the result of malloc().  It may 'hide' the bug of
 * a missing stdlib.h include, and cause troubles when
 * malloc() is implicitly defined by the compiler as:
 *
 *int malloc(...);
 *
 * On a 64-bit machine converting a 64-bit pointer to `int' will
 * lose the high-order 32 bits of the address, and you will try
 * to access unexpected memory areas.
 */
midataula = 3000;
missatge = malloc(midataula * sizeof(*missatge));
if (missatge == NULL)
err(1, malloc);

Then when you use realloc() keep both midataula and missatge in
temporary copies until you are sure that realloc() worked:

while (voltes  4) {
char *tmp;
size_t newsize;

newsize = midataula + 500;
tmp = realloc(missatge, newsize * sizeof(*missatge));
if (tmp == NULL)
err(1, realloc);

/*
 * Now that you know the resize has succeeded, update
 * midataula and missatge.  realloc() is allowed to
 * relocate missatge.  See the following note in its
 * manpage:
 *
 *   Note that realloc() and reallocf() may move the
 *   memory allocation, resulting in a different return
 *   value than ptr.
 */
midataula = newsize;
missatge = tmp;
}

Right now you are calling realloc() as:

realloc(missatge, newsize * sizeof(*missatge));

and throwing away the resulting pointer.  The first time that realloc()
discovers that the `resized' vector cannot fit in its original location,
it relocates the array, and returns the new location.  You throw away
that location and your next iteration through the loop tries to access
an invalid (already freed) memory region.

That's what causes your segmentation fault.

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Re: error allocating memory with realloc(). how can i increase max_allowed in the system? [solved]

2008-08-12 Thread Giorgos Keramidas 
On Tue, 12 Aug 2008 18:22:21 +0200, Jordi Moles Blanco [EMAIL PROTECTED] 
wrote:
 Hello,
 thank you very much for your time and help, i had completely
 misunderstood how realloc() works.

You are welcome, of course :-)

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Re: error allocating memory with realloc(). how can i increase max_allowed in the system?

2008-08-12 Thread Wojciech Puchar 

  realloc(missatge, midataula * sizeof(char));


should be

missatge=realloc(missatge, midataula * sizeof(char));

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