AllocationHeader is not copied from stack to the memory position

[talhasaruhan]

In StackAllocator you're doing this:

AllocationHeader allocationHeader{padding}; AllocationHeader * headerPtr = (AllocationHeader*) headerAddress; headerPtr = &allocationHeader;

Which doesn't copy the AllocationHeader object that's created on the stack into the memory position.

You should either use

memcpy(headerAddress, &allocationHeader, sizeof(AllocationHeader))

or just use placement new operator to create the object at the memory location.

I've tested this and just as I expected, you're actually getting garbage when you're reading the header in the Free function.

[prabhatg]

Is this warning ok?

src/StackAllocator.cpp:42:46: warning: narrowing conversion of 'padding' from 'std::size_t {aka long unsigned int}' to 'char' inside { } [-Wnarrowing]
AllocationHeader allocationHeader{padding};
^

[talhasaruhan]

Well, the author of the code defined AllocationHeader struct as follows (in the header file):

struct AllocationHeader {
        char padding;
    };

so when using list initialization, you're converting "padding" variable from size_t to char, which is theoretically not safe. BUT, since the actual padding will almost always fit into a char (meaning that it's integer value has to be less than 256) it'll work just fine. But if you're trying to align to huge blocks of memory, then padding may overflow.

So the best way to handle this depends on your use case, if you can assume that paddings before headers will always be less than or equal to 255, then you can just ignore the warning. But if you're trying to, for some reason align your blocks to huge chunks, say 512, then padding CAN overflow (or it may be undefined behavior, either case it's unsafe) so you should change the "char" in the definition to "size_t"