Question

I am having problems with an array which i want to re-use in my program. I need to change the size dynamically and clear it. But unfortunately the resizing does not work.

uint8_t * readBuffer; // Create array pointer

readBuffer = (uint8_t *) malloc(4); // Mem. alloc. 4bytes
memset(readBuffer, 0, sizeof(readBuffer); // Reset array
// Do stuff
free(readBuffer) // Release mem. block
....
readBuffer = (uint8_t *) malloc(1) // Mem. alloc. 1byte
memset(readBuffer, 0, sizeof(readBuffer); // Reset array
// Do stuff
free(readBuffer) // Release mem. block

At the the resizing step the length of my array is still the former (4).

Am i using free all wrong?

Further more is there much more efficient alternatives to memset for clearing?

Thanks in advance.

Answer 1

Size of a pointer (e.g. readBuffer) is always same (here 4 bytes) for any data type. You need to rather store the size given inside the malloc into a temporary and then use memset():

uint size = 4;
readBuffer = (uint8_t *) malloc(size); // Mem. alloc. 4bytes
memset(readBuffer, 0, size); // Reset array

Moreover argument to malloc() is in bytes, so malloc(1) means ideally 1 byte. If you are using C++ then use new:

readBuffer = new uint8_t[N];  // 'N' is number of elements of "uint8_t"

Edit:

In C++, std::vector provides this facility with much ease:

std::vector<uint8_n> readBuffer(N, 0);

Here you are allocating ‘N’ elements for readBuffer and initializing them to 0.
Whenever you want to add elements, you can use push_back() method. For bigger chunks you may also explore resize() or reserve() methods.