realloc vs malloc in C | 易学教程

问题

I'm fairly new to C, and just now starting to venture into the realm of dynamically allocated arrays.

I think i've got mostly malloc down, but had some questions on realloc:

Can realloc be used for anything else besides adding memory space to pointers?
Does the size variable always have to be an int?

Would something like the below work?

float *L = NULL;

int task_count = 5;

L = (float*) realloc (L, task_count * sizeof(float));

If I wanted to increase that space further (by one in this case), could I just use something like the following?

L = (float*) realloc (L, 1 * sizeof(float));

Seems deceptively simple, which tells me I'm possibly missing something.

回答1:

In case that ptr is a null pointer, the function behaves like malloc, assigning a new block of size bytes and returning a pointer to its beginning.

void * realloc (void* ptr, size_t size);

ptr - Pointer to a memory block previously allocated with malloc, calloc or realloc. Alternatively, this can be a null pointer, in which case a new block is allocated (as if malloc was called).

sizeNew - size for the memory block, in bytes. size_t is an unsigned integral type.

sizeNew has to define the entirety of the memory you want, could be smaller, could be larger!

回答2:

Yes, you can also reduce memory space
Nah, why that? It takes void* as 1st parameter and returns void*
Yes, but no need to cast!

And finally, you have to tell the total memory sizeto the function.

来源：https://stackoverflow.com/questions/22131381/realloc-vs-malloc-in-c

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malloc

realloc