What does this translate to...

[mark smit]

Hello,

I'm kinda brain dead today, can somebody please help me convert/translate this to PB?

unsigned char** imagefiles;

I'm just not sure how to deal with the "char**" its a pointer to a pointer but how would you write that in PB

imagefiles as asciiz ptr ptr

Thanks in advance!

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Cheers!

[Russ Srole]

Mark,

I'm not a C guy, so someone may shoot me down on this one, but I
did run into that sort of thing with a dll I was using.

I think it's really:
Char **imagefiles
and what you do is:
dim MyString as asciiz * 256
dim MyStPtr as String Ptr
dim MyP2P as long
MystPtr = varptr(Mystring)
MyP2P = MyStPtr
declare Whatever(byref MyP2P as long)
Call Whatever(MyP2P)

Why they do this is beyond me. I certainly never got a straight
answer when I asked. And the dll I was calling had plenty of
pointers to string (so they could fill with data), but only one
pointer to a pointer. Please, Oh gurus of C, explain it to all
of us!

Later,
Russ Srole

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[Steve Hutchesson]

Mark,

This is off the top of my head and I have no way to test it but
with the extra level of indirection, I would be inclined to try
something like this to read it.

! mov eax, The_Double_Ptr
! mov eax, [eax] ; dereference it once
! mov eax, [eax] ; and once more
! mov Where_Its_At, eax

To write the value if you are passing it to a function,

First_Level_Of_Indirection = VarPtr(MyVar)
Second_Level_Of_Indirection = VarPtr(First_Level_Of_Indirection)

This may do the job for you but at least it gives you the general idea.

Regards,

[email protected]



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[mark smit]

Thanks Guys!


But here's the problem.

typedef struct IMAGE {
    unsigned char** imagefiles;
} IMAGE;

How do I convert this into a PB TYPE? This is about as close as I can come up with. But this still doesn't provide the exact same thing as the C example.

type IMAGE
    imagefiles as asciiz ptr
end type

How would you define a member inside a TYPE that is a pointer to another pointer?


Thanks again guys!


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Cheers!

[Daniel Corbier]

I think in this context, char** imagefiles; represents a string
array for imagefiles. So imagefiles[0], and imagefiles[1], etc...
would be the array elements representing the first few files. They
could have used char* imagefiles[] just the same. In C, you
don't really have native strings. So you use either an array of
characters to represent a string, or a pointer to those characters.

Now for an array of strings, you'd need either an array of that
array (a two-dimensional array) or a pointer to char array,
or else a pointer to the pointer. unsigned char simply
means that you can go from 0 255, instead -128 to 127. I'm not
sure why people would use ** in this context. But I've seen the
argv argument for the main() function sometimes defined as
char **argv, and other times as char * argv[].

Fortunately strings are much easier to deal with in BASIC.
Although I haven't tried it, my guess would be that this would
translate to PB simply as an ASCIIZ array.

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Daniel Corbier
UCalc Fast Math Parser
http://www.ucalc.com