Im newbie

[shekel]

Hi, my name is shekel and im from spain.. english is not my native language, so excusme if its difficult understand me.

I read the Iczelon's tutorials and i can understand all the code.. but now im trying to do something in asm for myself.

This is c++.. how can I do this in asm?

String var = "-Hello World-";
String var2 = var.substr(1, var.size() - 2);

This code remove the first and the last character, in asm i need duplicate the string and modify the result??? or can i mov into "esi" the string with a start and end position without "break" the original string?

Sorry by my english

[dedndave]

Code Select Expand

String var = "-Hello World-";

that one is easy enough
if it's global data, and assuming it is zero terminated...

Code Select Expand

    .DATA

var     db "-Hello World-",0

if it's local data, you can assign a buffer, but you have to put the string into the buffer, "manually"

Code Select Expand

MyFunc PROC

    LOCAL   var[16]   :BYTE

    mov dword ptr var,"leH-"
    mov dword ptr var+4,"W ol"
    mov dword ptr var+8,"dlro"
    mov word ptr var+12,"-"

;
;
    ret

MyFunc ENDP
there's probably a macro to do that - or there should be   :P

this one's a bit different - it requires that you execute some code
normally, we would write a function to perform the operation, and pass pointers to the string and buffer, and perhaps a length

Code Select Expand

String var2 = var.substr(1, var.size() - 2);
there's probably also a macro for that

but, to copy a string, i might use the string instructions

Code Select Expand

    push    esi
    push    edi
    mov     esi,<address of source>
    mov     edi,<address of destination>
    mov     ecx,<number of elements to copy>    ;bytes, words, or dwords
    rep     movsb                               ;or movsw for words, or movsd for dwords
    pop     edi
    pop     esi
you can modify that, as required, to copy only the bytes you want into the destination buffer

[jj2007]

Dave is a bit demanding today

Here is a simpler approach:

Code Select Expand

include \masm32\include\masm32rt.inc

.data
var1 db "-Hello World-", 0
var2 db 100 dup(?) ; generous buffer for the copy

.code
start:
  mov esi, offset var1
  mov edi, offset var2
  inc esi
  mov ecx, sizeof var1-3 ; subtract 1 for the inc esi, 1 for the right end, and 1 for the zero delimiter
  rep movsb
  inkey offset var2
  exit

end start

Read \Masm32\help\opcodes.chm to understand rep movsb

And have a look at this two-pager, too.