sizeof(udt) and more

[Fabrizio_00000]

Hi guys, please help me out because this thing is driving me crazy.

Have a look at this code fragment:

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type flddef field = 1
	name	as string * 16
	namelen	as ubyte
	type	as ubyte
	size	as ushort
end type

print sizeof(flddef)

I should get 20 (16 + 1 + 1 + 2) but the result is 21. Why?

But there's more:

I have a string whose content ("outstr", whose length is 100 bytes) is what should be passed into flddef with these lines of code:

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recdef = allocate(5 * sizeof(flddef))
for i = 0 to 4
	memcpy(@recdef[i], sadd(outstr) + i * 20, sizeof(flddef))
next

The transfer takes place successfully, in fact the verification of the content of the allocated memory area is correct:

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for i = 0 to flds * sizeof(flddef) - 1
	ch = *(cast(ubyte ptr, recdef) + i)
	print hex(ch, 2); " ";
	linlen += 1
	if linlen = sizeof(flddef) then
		linlen = 0
		print
	endif
next
print

Result:

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41 4C 50 48 41 30 30 30 30 30 30 30 30 30 30 31 D0 10 0A 00 42
42 45 54 41 30 30 30 30 30 30 30 30 30 30 30 32 10 02 02 00 47
47 41 4D 4D 41 30 30 30 30 30 30 30 30 30 30 33 90 03 04 00 44
44 45 4C 54 41 30 30 30 30 30 30 30 30 30 30 34 10 08 04 00 45
45 50 53 49 4C 4F 4E 30 30 30 30 30 30 30 30 35 10 10 14 00 00

The last byte of each record seems to be the first of the next one (do you remember? 21 instead of 20). But let's leave this issue out for now. Let's try to inspect the individual fields:

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for i = 0 to flds - 1
	print recdef[i].name; " "; recdef[i].namelen; " "; recdef[i].type; " "; recdef[i].size
next

The result should have been this:

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ALPHA00000000001 208 16 10
BETA000000000002 16 2 2
GAMMA00000000003 144 3 4
DELTA00000000004 16 8 4
EPSILON000000005 16 16 20

But instead this is what I get:

Code: Select all

ALPHA00000000001 16 10 16896
BETA000000000002 2 2 18176
GAMMA00000000003 3 4 17408
DELTA00000000004 8 4 17664
EPSILON000000005 16 20 0

it seems that the "namelen" field is completely ignored.

I'm considering getting help from a good psychiatrist but thought maybe I'm not the problem...

[fxm]

From documentation:

Fixed length strings are also terminated with a NULL character, and so they use size + 1 bytes of space. This NULL terminator may be removed in future, to prevent the redundant character complicating data layout in user-defined Types.

[Fabrizio_00000]

Oh, God! I'll have to rewrite 80% of my code...
Well, at least I learned something.
Thanks, fxm!

[fxm]

NOTE:

'Dim As String * n ...':
- total characters = n+1
- useful characters = n

'Dim As Zstring * n ...' or 'Dim As Wstring * n ...' :
- total characters = n
- useful characters = n-1