malloc address

[Max]

I am trying to print the memmory address that malloc allocates
AND print the memory address that has been freed.

how do I do that?

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int main (void)
{
	char *pt;

	pt=(char*)malloc(40);
	if (pt==NULL)
		{
		perror("dynline1");
		exit(1);
		}

	strcpy(pt, "abcdefghijklmnopqrstuvxyz");
	puts(pt);

	free(pt);

	return 0;
}

[hk_mp5kpdw]

Its been awhile, but maybe:

printf("Address is %p.\n",pt);

This will let you print out the address stored in the pt variable.

[The Dog]

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int main (void)
{
	char *pt;

	pt=(char*)malloc(40);
	if (pt==NULL)
		{
		perror("dynline1");
		exit(1);
		}

	strcpy(pt, "abcdefghijklmnopqrstuvxyz");
	printf("%p", pt);

	free(pt);

	return 0;
}

In C you don't have to cast malloc().

[Max]

Thanks......and how can I print the address freed after free(pt)

[The Dog]

The pointer that you allocated memory to is also the one that you free'd.

char *pt;
pt = malloc(40);
printf("%p",pt);
free(pt);         //You've already printed it's address

[Dave_Sinkula]

Some additional information...

http://www.eskimo.com/~scs/C-faq/q7.21.html
When you call free, the memory pointed to by the passed pointer is freed, but the value of the pointer in the caller remains unchanged, because C's pass-by-value semantics mean that called functions never permanently change the values of their arguments.

A pointer value which has been freed is, strictly speaking, invalid, and any use of it, even if is not dereferenced can theoretically lead to trouble, though as a quality of implementation issue, most implementations will probably not go out of their way to generate exceptions for innocuous uses of invalid pointers.

[The Dog]

Originally posted by Dave_Sinkula
Some additional information...

A pointer value which has been freed is, strictly speaking, invalid, and any use of it, even if is not dereferenced can theoretically lead to trouble, though as a quality of implementation issue, most implementations will probably not go out of their way to generate exceptions for innocuous uses of invalid pointers.

Which is why it's so very good to NULL your pointers after you free them.

char* ptr = malloc(50);
free(ptr);
ptr = NULL;

[Sayeh]

In C you don't have to cast malloc().

Actually this is not correct. Using type coercion on malloc() has not so much to do with C as it has to do with the compiler you are using.

The older the compiler, the more likely it flag a 'pointer mismatch' unless you've coerced.

---

It does ABSOLUTELY NO HARM to use type coercion. If anything, it allows for a wider portability to older platforms or compilers because nothing is left to chance.

[moi]

Originally posted by Sayeh
Actually this is not correct. Using type coercion on malloc() has not so much to do with C as it has to do with the compiler you are using.

The older the compiler, the more likely it flag a 'pointer mismatch' unless you've coerced.

---

It does ABSOLUTELY NO HARM to use type coercion. If anything, it allows for a wider portability to older platforms or compilers because nothing is left to chance.

dont waste your time decapitating your programs for pre-ansi-c89 compilers.