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Accessing Array from ASM passed from C++?

Of1983vintage

Subject: Accessing Array from ASM passed from C++? · Posted: 2006-11-26, 05:21pm

Rank: ? (1)
Member #: 29207

I've been studying assemby for about a semester now. I am having a horrible time figuring out how to access the array of data I pass from C++ to ASM. It is a array of strings which I will have to sort in ASM and return a sorted array back to C++. The biggest problem I am having is accessing the data itself. The array is being passed at [ebp+8]... Any help with this is appreciated.

This is the C++ code I'm working with;
Code:

extern "C" int Sort (char [] [20], int, int);

Code:

Sort (Strings, 10, 20);
cout << "Sorted Strings are" << endl;
for (i = 0; i < 10; i++)
cout << '\t' << Strings [i] << endl;

You can probably ignore my code, but I figure I would put it anyways;
Code:

_Sort proc
push ebp
mov ebp, esp
push edi
mov eax, [ebp+08]
mov array_ptr, eax
mov eax, [ebp+12]
mov array_length, eax
mov eax, [ebp+16]
mov bytes_per_line, eax
mov eax, array_length
cmp eax, 0 ;jump if array has length of 0
jnae EndTRow
mov ebx, found_length
inc ebx ;add 1 to found_length's sum
cmp ebx, eax ;jump if at last row
ja EndTrow
; mov found_length, ebx
Tcolumns:
mov eax, char_position
mov ebx, bytes_per_line
cmp eax, ebx
jnb TRows
... ...and it becomes useless jargon here
EndTrow:
pop edi
pop ebp
ret
_Sort endp

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igorok

Subject: Re: Accessing Array from ASM passed from C++? · Posted: 2006-12-23, 09:55pm

Rank: ? (119)
Member #: 28292

You should put the pointer passed to stack in a register. For example edx. For addressing of an element of array of chars use e.g. byte ptr [edx + ecx]. In ecx is the number of the element you want to use.

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