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Hello,

I create a pointer, get some memory with calloc, but when I want to free
it, I get a run-time error.

Here is the code:

char *script;
script = scalloc(71,sizeof(char));
script="/cm {72 mul 2.54 div} def\n1 cm 1 cm scale\n0.014
setlinewidth\n0 setgray\n";
fprintf(image_file,script);
fclose(image_file);
// free(script);

image_file is defined elsewhere, and there isn't any problem with it.

Note: I read the FAQ at
http://www.eskimo.com/~scs/C-faq/top.html

Thanks for help.

And if my questions does irritate you, please don't respond...

Oodini wrote:
> Hello,
>
> I create a pointer, get some memory with calloc, but when I want to free
> it, I get a run-time error.
>
> Here is the code:
>
> char *script;
> script = scalloc(71,sizeof(char));
> script="/cm {72 mul 2.54 div} def\n1 cm 1 cm scale\n0.014
> setlinewidth\n0 setgray\n";
> fprintf(image_file,script);
> fclose(image_file);
> // free(script);
>
> image_file is defined elsewhere, and there isn't any problem with it.

Oodini...

Note that when you assigned a pointer to the string "/cm... " to
script, you destroyed the pointer returned from calloc(). You
aren't, of course, entitled to free the space occupied by that
string literal.

<OT> Did you really mean "0.014 cm setlinewidth"? 0.014 pt might
as well be zero.
</OT>

--
Morris Dovey
West Des Moines, Iowa USA
C links at http://www.iedu.com/c

In article <>, Oodini wrote:
> Hello,
>
> I create a pointer, get some memory with calloc, but when I want to free
> it, I get a run-time error.
>
> Here is the code:
>
> char *script;
> script = scalloc(71,sizeof(char));

What is scalloc?

I'm going to pretend you said malloc.

> script="/cm {72 mul 2.54 div} def\n1 cm 1 cm scale\n0.014
> setlinewidth\n0 setgray\n";

You have overwritten your pointer from malloc with a pointer to
a literal string. When you pass this pointer to free, worlds
collide.

--
Neil Cerutti

>>char *script;
>>script = scalloc(71,sizeof(char));
>
> What is scalloc?

A "safe calloc" function (it checks if calloc receives NULL).

>>script="/cm {72 mul 2.54 div} def\n1 cm 1 cm scale\n0.014
>>setlinewidth\n0 setgray\n";
>
>
> You have overwritten your pointer from malloc with a pointer to
> a literal string. When you pass this pointer to free, worlds
> collide.

Actually, my goal was to put the string in the pointer.
I didn't thought it wil use an other memory space.

What do you suggest ?
Should I use only a string, and wait for its destruction at the end of
the function, or copy the string to the pojnter in an other way ?

Thanks.

>> char *script;
>> script = scalloc(71,sizeof(char));
>> script="/cm {72 mul 2.54 div} def\n1 cm 1 cm scale\n0.014

> Note that when you assigned a pointer to the string "/cm... " to script,
> you destroyed the pointer returned from calloc(). You aren't, of course,
> entitled to free the space occupied by that string literal.

That was the point.
Thanks.

>>char *script;
>>script = scalloc(71,sizeof(char));


> assuming calloc(), you have initialized this pointer with the value returned
> by calloc() which is the address of a freshly allocated block. All bits are
> set to zero. Note that sizeof(char) is 1 by-definition. How did you specify
> 71? Isn't it a better way of doing it? I mean automagically (strlen, sizeof
> etc.)

Please don't laugh: I counted them.
To use strlen, I have to create a string.
But my goal was to create a pointer to free it later.
Not really needed (a string would be OK).
But may I free a string ?? I don't think so...

> The value passed to free() must be exactly the one you got from malloc() (or
> one of its brothers). You have changed it, creating a memory leak, hence the
> undefined behaviour.

OK. i got it now. Thanks.

In article <>, Oodini wrote:
>>>char *script;
>>>script = scalloc(71,sizeof(char));
>>
>> What is scalloc?
>
> A "safe calloc" function (it checks if calloc receives NULL).
>
>>>script="/cm {72 mul 2.54 div} def\n1 cm 1 cm scale\n0.014
>>>setlinewidth\n0 setgray\n";
>>
>> You have overwritten your pointer from malloc with a pointer
>> to a literal string. When you pass this pointer to free,
>> worlds collide.
>
> Actually, my goal was to put the string in the pointer. I
> didn't thought it wil use an other memory space.

You can only store the address of things in pointers. You can't
store anything in pointers except pointers.

> What do you suggest ?

Copy the string into the storage pointed to by script using
strcpy.

strcpy(script, "/cm {72 mul 2.54 div}...");

--
Neil Cerutti

On Fri, 27 Jun 2003 17:25:46 +0200, Oodini wrote:

> Hello,
>
> I create a pointer, get some memory with calloc, but when I want to free
> it, I get a run-time error.
>
> Here is the code:
>
> char *script;
> script = scalloc(71,sizeof(char));

What is this 'scalloc'?

> script="/cm {72 mul 2.54 div} def\n1 cm 1 cm scale\n0.014

Strings must be on one line. I'll assume your newsreader broke this line.

> setlinewidth\n0 setgray\n";

You don't copy strings like that. You just lost the memory you allocated
(literally!)

You meant:

strcpy(script, "...");

Also, you need to allocate one extra character, for the terminating null.
Here's how I'd do it:
const char *orig = "/cm {72 mul 2.54 div} def\n1 cm 1 cm scale\n0.014 "
"setlinewidth\n0 setgray\n";
char *script;
script = malloc(strlen(orig) + 1);
if(!script){
fprintf(stderr, "Unable to allocate memory\n");
exit(EXIT_FAILURE);
}
strcpy(script, orig);

> fprintf(image_file,script);
> fclose(image_file);
> // free(script);

Why'd you copy it? Just use:
fprintf(image_file, "...");
and get rid of the script variable.

--
Freenet distribution not available
Teutonic:
Not enough gin.

On Fri, 27 Jun 2003 19:30:34 +0200, Oodini wrote:

>>>char *script;
>>>script = scalloc(71,sizeof(char));
>
>
>> assuming calloc(), you have initialized this pointer with the value returned
>> by calloc() which is the address of a freshly allocated block. All bits are
>> set to zero. Note that sizeof(char) is 1 by-definition. How did you specify
>> 71? Isn't it a better way of doing it? I mean automagically (strlen, sizeof
>> etc.)
>
> Please don't laugh: I counted them.
> To use strlen, I have to create a string.

strlen("I am a string literal. I can be used in strlen") works.
Also,
const char *foo = "I am a string literal.";
strlen(foo);
works.

> But my goal was to create a pointer to free it later.
> Not really needed (a string would be OK).
> But may I free a string ?? I don't think so...

Nope, but there's no reason to. Your memory usage increases if you
manually allocate somewhere to put a copy - string literals are never
freed.

>
>> The value passed to free() must be exactly the one you got from malloc() (or
>> one of its brothers). You have changed it, creating a memory leak, hence the
>> undefined behaviour.
>
> OK. i got it now. Thanks.

--
Freenet distribution not available
There's no saint like a reformed sinner.

On Fri, 27 Jun 2003 19:26:29 +0200, Oodini wrote:

>>>char *script;
>>>script = scalloc(71,sizeof(char));
>>
>> What is scalloc?
>
> A "safe calloc" function (it checks if calloc receives NULL).
>
>>>script="/cm {72 mul 2.54 div} def\n1 cm 1 cm scale\n0.014
>>>setlinewidth\n0 setgray\n";
>>
>>
>> You have overwritten your pointer from malloc with a pointer to
>> a literal string. When you pass this pointer to free, worlds
>> collide.
>
> Actually, my goal was to put the string in the pointer.
> I didn't thought it wil use an other memory space.
>
> What do you suggest ?
> Should I use only a string, and wait for its destruction at the end of
> the function, or copy the string to the pojnter in an other way ?

The correct way to copy a string is using strcpy:
strcpy(destination, source);

There must be room for strlen(source) + 1 chars in destination.

--
Freenet distribution not available
As he had feared, his orders had been forgotten and everyone had brought
the potato salad.