Is Realloc safe?

Why is Realloc bad?

In Standard C, realloc is an infamous example of bad design. It has to do too many things: allocate memory if passed NULL, free it if passed a zero size, reallocate it in place if it can, or move memory around if it cannot. It is not easily extensible. It is widely viewed as a short-sighted design failure.

Can Realloc fail?

The chances that malloc or realloc fail are negligible on most modern system. This only occurs when you run out of virtual memory. Your system will fail on accessing the memory and not on reserving it. W.r.t failure realloc and malloc are almost equal.

Is Realloc thread safe?

3p2 confirms that malloc, calloc, realloc, aligned_alloc, and free in particular are thread-safe: For purposes of determining the existence of a data race, memory allocation functions behave as though they accessed only memory locations accessible through their arguments and not other static duration storage.

Is Realloc expensive?

4 Answers. A realloc isn’t really very expensive. But calling realloc for each element is a bit much.

Does Realloc copy memory?

Yes, realloc retains the contents of the item of which memory is reallocated. From the realloc man page: Quote: realloc() changes the size of the memory block pointed to by ptr to size bytes.

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Does Realloc free the old block?

Secondly, if realloc decided to follow the first approach (i.e. allocate a new memory block), then the old block is indeed freed by realloc . In that case trying to access the original memory location leads to undefined behavior. … It can’t really be used to analyze whether the behavior is «proper».

What happens if Realloc fails?

If realloc() fails the original block is left untouched; it is not freed or moved.

Does Realloc have zero memory?

Just as is the case with malloc , realloc doesn’t perform any initialization. Any memory past the memory that was present in the original block is left uninitialized. You may have to initialize the new space. … Therefore, simply initialising the memory to zero could invoke undefined behaviour.

How do I use Realloc?

Use of realloc()

Size of dynamically allocated memory can be changed by using realloc(). As per the C99 standard: void * realloc ( void *ptr, size_t size); realloc deallocates the old object pointed to by ptr and returns a pointer to a new object that has the size specified by size.

Does Realloc erase data?

If you’re merely asking whether the old contents will be preserved at the new address returned by realloc , the answer is yes (up to the minimum of the old size and the new size).

Can Realloc be used without malloc?

malloc is not required, you can use realloc only. malloc(n) is equivalent to realloc(NULL, n) . However, it is often clearer to use malloc instead of special semantics of realloc . It’s not a matter of what works, but not confusing people reading the code.

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Do you need to free after Realloc?

Once you call realloc() , you do not have to free() the memory addressed by pointer passed to realloc() — you have to free() the memory addressed by the pointer realloc() returns. (Unless realloc() returns NULL , in which case the original block of memory — passed to realloc() — has to be free() ‘d.)