bugIntroducedDebugging

[u/ClipboardCopyPaste]

[u/AdBrave2400]

Is the mistake that they're allocating 1 byte and storing in a pointer to an int which is 4 bytes?

[u/atanasius → u/AdBrave2400]

It's allowed to assign to a pointer if it's not dereferenced. Malloc always returns a valid pointer.

[u/vishal340 → u/atanasius]

but accessing it will be issue right?

[u/backfire10z → u/vishal340]

Likely not. Malloc guarantees that the passed-in size is the minimum number of bytes it allocates, but not the maximum. You’d likely get some minimum sized chunk, somewhere between 16-32 bytes depending on the system as far as I understand it.

[u/atanasius → u/backfire10z]

Implementations are allowed to specify behavior that is otherwise undefined.

I looked up a C24 draft and it's actually stricter:

The pointer returned if the allocation succeeds is suitably aligned so that it may be assigned to a pointer to any type of object with a fundamental alignment requirement and size less than or equal to the size requested.

So a pointer returned by malloc(1) is not necessarily valid for int*.

[u/p88h → u/atanasius]

Aligned means int sized at minimum.

The actual allocated size is much bigger anyways, but it will be a multiple of 8 bytes on a 64 bit system, and 'usable' part of that will be at least 8 bytes, and typically you will be able to read at least 16 without a page fault.