On Sunday, 4 December 2022 at 17:27:39 UTC, Nick Treleaven wrote:
On Sunday, 4 December 2022 at 16:33:35 UTC, rempas wrote:
(MemoryBlock.sizeof is 16 on my 64-bit system).
The above adds 16 bytes to ptr.
The above adds 16 * MemoryBlock.sizeof bytes (16 * 16) to ptr,
because ptr is cast first. Should be `+ 1` to be equivalent.
https://dlang.org/spec/expression.html#pointer_arithmetic
"the resulting value is the pointer plus (or minus) the second
operand **multiplied by the size of the type pointed to by the
first operand**."
Thanks! This explains it. And I have tried and I can only use "+"
or "-" with a pointer so it explains it.
char* return_address_wrong() {
MemoryBlock* local_ptr = cast(MemoryBlock*)ptr;
return cast(char*)(local_ptr + MemoryBlock.sizeof); //
Casted the whole expression. BUT GOT THE WRONG VALUE!!!! Why???
}
Because you are adding to a pointer that points to a 16-byte
block, rather than a void* which points to a single byte.
char* return_address_right() {
MemoryBlock* local_ptr = cast(MemoryBlock*)ptr;
return cast(char*)local_ptr + MemoryBlock.sizeof; // Now I
first casted the `local_ptr` variable and then added the
number but this time this gave me the right value....
}
The casted pointer points to a single byte.
I think I get it! The first part about the arithmetic explains it
all well. I was also able to fix my program. They way I see it,
you return from a function by first casting the first operand and
when you want to get a variable (or pass one to a function), you
cast the whole expression. At least that's how it worked with my
program.
