free – Tarik Billa

Allocate memory and save string in c

April 8, 2024 by Tarik

char *test = (char*) malloc(12*sizeof(char)); +-+-+-+-+-+-+-+-+-+-+-+-+ test—>|x|x|x|x|x|x|x|x|x|x|x|x| (uninitialized memory, heap) +-+-+-+-+-+-+-+-+-+-+-+-+ test = “testingonly”; +-+-+-+-+-+-+-+-+-+-+-+-+ test + |x|x|x|x|x|x|x|x|x|x|x|x| | +-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+ +->|t|e|s|t|i|n|g|o|n|l|y|0| +-+-+-+-+-+-+-+-+-+-+-+-+ free(test); // error, because test is no longer pointing to allocated space. Instead of changing the pointer test, you need to copy the string “testingonly” into the allocated place using e.g. … Read more

Does malloc reserve more space while allocating memory?

December 20, 2023 by Tarik

Once free()-d, I am expecting program’s virtual memory (VIRT) consumption to be down by 1MB. Well, this is not guaranteed by the C standard. It only says, once you free() the memory, you should not be accessing that any more. Whether the memory block is actually returned to the available memory pool or kept aside … Read more

LinkedList – How to free the memory allocated using malloc

December 10, 2023 by Tarik

The usual way is with (pseudo-code first): node = head # start at the head. while node != null: # traverse entire list. temp = node # save node pointer. node = node.next # advance to next. free temp # free the saved one. head = null # finally, mark as empty list. The basic … Read more

malloc implementation?

December 5, 2023 by Tarik

The easiest way to do it is to keep a linked list of free block. In malloc, if the list is not empty, you search for a block large enough to satisfy the request and return it. If the list is empty or if no such block can be found, you call sbrk to allocate … Read more

Proper Way to Free Memory of a Returned Variable

September 22, 2023 by Tarik

It’s quite simple, as long as you pass to free() the same pointer returned by malloc() it’s fine. For example char *readInput(size_t size) { char *input; int chr; input = malloc(size + 1); if (input == NULL) return NULL; while ((i < size) && ((chr = getchar()) != ‘\n’) && (chr != EOF)) input[i++] = … Read more

double free or corruption (!prev) error in c program

September 22, 2023 by Tarik

double *ptr = malloc(sizeof(double *) * TIME); /* … */ for(tcount = 0; tcount <= TIME; tcount++) ^^ You’re overstepping the array. Either change <= to < or alloc SIZE + 1 elements Your malloc is wrong, you’ll want sizeof(double) instead of sizeof(double *) As ouah comments, although not directly linked to your corruption problem, … Read more

C free(): invalid pointer

September 17, 2023 by Tarik

You’re attempting to free something that isn’t a pointer to a “freeable” memory address. Just because something is an address doesn’t mean that you need to or should free it. There are two main types of memory you seem to be confusing – stack memory and heap memory. Stack memory lives in the live span … Read more

Can I assume that calling realloc with a smaller size will free the remainder? [duplicate]

August 15, 2023 by Tarik

Yes, guaranteed by the C Standard if the new object can be allocated. (C99, 7.20.3.4p2) “The realloc function deallocates the old object pointed to by ptr and returns a pointer to a new object that has the size specified by size.”

Is free() zeroing out memory?

August 13, 2023 by Tarik

There’s no single definitive answer to your question. Firstly, the external behavior of a freed block will depend on whether it was released to the system or stored as a free block in the internal memory pool of the process or C runtime library. In modern OSes the memory “returned to the system” will become … Read more

Should I free memory before exit?

July 23, 2023 by Tarik

This is actually a really hard, imponderable question. Pro (in favor of freeing everything before exit): no bugs or memory leaks later if code is rearranged no false positives from valgrind or memory leak checker no memory leaks if you’re running under a buggy OS, or no OS at all Con (just exit, don’t worry … Read more