Setting a buffer of char* with intermediate casting to int*

Question

I could not fully understand the consequences of what I read here: Casting an int pointer to a char ptr and vice versa

In short, would this work?

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Answer 1

Use reinterpret_cast<>() if you want to ensure the underlying data does not "change shape".

As Learner has mentioned, when you store data in machine memory endianess becomes a factor. If you know how the data is stored correctly in memory (correct endianess) and you are specifically testing its layout as an alternate representation, then you would want to use reinterpret_cast<>() to test that memory, as a specific type, without modifying the original storage.

Below, I've modified your example to use reinterpret_cast<>():

void set4Bytes(unsigned char* buffer) {
  const uint32_t MASK = 0xffffffff;
  if (*reinterpret_cast(buffer) % 4) {//misaligned
     for (int i = 0; i < 4; i++) {
       buffer[i] = 0xff;
     } 
  } else {//4-byte alignment
    *reinterpret_cast(buffer) = MASK;
  }
}

It should also be noted, your function appears to set the buffer (32-bytes of contiguous memory) to 0xFFFFFFFF, regardless of which branch it takes.