Thread: a noob freeing memory...

supposed we have a this

Code:

int func(){
   int *p;

   p=malloc(some,sizeof some);

   return something_else;
}

lets suppose we don't free() the allocated memory. what happens with the allocated space when we call again the function??? is it freed or do we have n-allocations for n-function-calls???

Originally Posted by Prelude

>is it freed or do we have n-allocations for n-function-calls???
Yes. This is called a memory leak.

i can guess that there will be problems if i free(p) and try to return p with int *f() ???

Originally Posted by Prelude

>i can guess that there will be problems if i free(p) and try to return p with int *f() ???
Good guess. That has a special name too, it's a dangling pointer.

is there any way to retrieve the pointer value externally while being able to free the memory it allocates? i guess that when the function returns all the allocated space will be unreachable to free().

Originally Posted by Prelude

>is there any way to retrieve the pointer value externally while being able to free the memory it allocates?
Return the pointer. Basically, as long as you have a pointer to the memory, you're capable of freeing it, regardless of whereever in the code you are. Once you lose the last reference to the memory, you've leaked it.

thanks alot!!!

i want to initialise,return and free a variable length 2-d array...
suppose i do this:

Code:

int **f(some input){

  int **p;
  p=malloc(dim_1*sizeof(int *));
	
  for(i=0;i<dim_2;i++)	p[i]=malloc(dim_1*sizeof(int));

  blah blah blah...

  return p;
}

first of all, is my initialization right? is there anything illegal in it? it surely works for me but is there a more right way to do it?

secondly how do i free tis pointer if i return it in main??? i have tried many ways but still i run valgrind mem test on my code and get memory leaks...

if i dont return i do this inside my function and have no problems:

Code:

for(i=0;i<dim_2;i++)	free(p[i]);
free(p);

no memory leaks nothing...

but if i do the same thing outside the function with its reference i still get memory leaks.
any suggestions?
thanks

i did as you said. it really works internally but when i free it from main i still get leaks.
any suggestions? i would post code but its pretty huge. i'll try to cut things out and maybe post it...

Originally Posted by swoopy

>i did as you said. it really works internally but when i free it from main i still get leaks.
>any suggestions?
It sounds like the memory for your array is getting corrupted at some point after the malloc and before the free. You could print the array at various points in main to see where the corruption occurs.

if i don't free in main the code seems to leak exactly the double amount of bytes. doesn't this mean that the memory allocated in int **f() is never freed? but i can't free it before i return it.