Changing from dynamic memory to static memory

Question

I'm trying to change a dynamic memory object to static memory use to hopefully free up memory in a way.

Original code(dynamic):

Class.h:

Class() {
  auto output = std::unique_ptr<uint8_t[]>(new uint8_t[size]);

  Call(output.get());
  memcpy(randomlocation, output.get(), size);
}

Call(Byte *dest) {
  doStuff..
}

I'm very confused how I can do a similar .get() but with a non unique-ptr. I've seen &* may work but haven't had any luck.

My trial of static:

Class.h:

uint8_t *output[64];

Class() {
  Call(reinterpret_cast<Byte*>(&*output));
}

I have tried other ways like no &* and different ways of casts and haven't had any luck. It compiles sometimes, but doesn't seem to work right. Wanting to see if this part is wrong, if not then I will at least know I'm doing this part right.

I'm trying to change a dynamic memory object to static memory use to hopefully free up memory in a way. Remember that static memory is usually much more limited than dynamic memory. Normally you only have access to a small number of MB of static memory while dynamic memory has a much higher limitation. — drescherjm
– drescherjm, Commented Aug 23, 2023 at 17:14
Why? What is actual problem? This smells like XY problem. Why your attempt is uint8_t *output[64]; not Byte output[64]; or better std::array<Byte, 64> output;? Note global state usually means fragile code. — Marek R
– Marek R, Commented Aug 23, 2023 at 17:17
uint8_t *output[64]; -- This declares an array of 64 pointers. Is this your intention? — PaulMcKenzie
– PaulMcKenzie, Commented Aug 23, 2023 at 17:21
Note having to use "reinterpret_cast" is almost always wrong when pointers are involved. And memcpy is kind of a legacy "C" thing, in C++ it is best replaced with std::copy — Pepijn Kramer
– Pepijn Kramer, Commented Aug 23, 2023 at 18:03

Remy Lebeau · Accepted Answer · 2023-08-23 19:55:01Z

1

Use uint8_t output[64]; instead. The output is like uint8_t* to 64 bytes of static memory.

This works:

void cal(uint8_t* dest)
{
    ...
}

uint8_t output[64];    
cal(output);

edited Aug 23, 2023 at 19:55

Remy Lebeau

609k36 gold badges516 silver badges875 bronze badges

answered Aug 23, 2023 at 17:28

Boris Radonic

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