well basicly i was haveing a look at someone''s source code, a bit of it actually, and i saw this wierd __asm thing. i looked on msdn and apparently it allows u to write in assembly but, as we all know msdn is not for learning but rather looking things up. i had a little search on google, 1/2 an hours worth, and found nothing really apart from that there is AT&T and INTEL versions and i think VC++.NET uses INTEL version of __asm{}. does anyone know where i can find proper matterial on this __asm{} block and how to use it? thanx for reply.

Simply :


int A = 6, B = 0;
__asm {
mov ax, A
mov B, A
}
printf("B has stored : %i\n", B);
// The output is 6

there are plenty of assembly tuts out there enter "Assembly tutorial" or *Assembler tutorial" (both without quotes) @ google.com . But although Leyder Dylan's assembley itself may be wrong, the structure is correct

//strncpy routineint nchar *src,*dest__asm {  mov ecx,n //counter  mov si,offset src //source address  push ds //moving ds into es  pop es  mov di,offset dest //destingation address  rep movsb //decrement ecx, if it isn't 0, mov ds:si to es:di} 

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Regret Nothing - Learn Everything

[edited by - NeViL tHe dEVil on October 3, 2003 4:03:40 AM]

NeViL tHe dEVil wat does push es mean, i recon push is a keyword but es has not been defined, this is all very confusing like push is like assingment, and pop is delet that address right?! but why are u doing all this es di stuff?

k ill look on google.com for this assembler tutorials, but isnt assembler hardware specific, so i cant use assembler for intel on AMD?

Assembler is not very hardware-specific, since ALL programs are turned into assembler before they are turned into machine code. I myself have a AMD Duron and it all works fine. I''m not sure how it works on MACs though. Also, DOS and UNIX may have different interrupt systems. To explain what I wrote:

Command mov destination,source
moves the contents of source into destination. source and destination can be registers, addresses and labels.

command push and pop
push: moves a value onto the stack. I f you don''t know wht the stack is, read any book about programming
pop: moves the last value pushed onto the stack back off it
The stack is defined by the registers ss:sp

command rep movsb
is infact to commands:

command rep
executes the following command (wich must be from the movs,lods or stos (= movestring,loadstring or storestring) family) and decrements ecx. it repeats this until ecx is 0

command movsb
from the family movs
mov = move; s = string; b = byte
moves one byte from ds:si to es:di. Thats the reason why I moved the offsets of the strings into si and di and made es = ds. However, ''mov'' cannot be applied to ds and es at the same time, so it''s faster to use push and pop.

Hope this helped you

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Regret Nothing - Learn Everything

Thanks for you infos. That was just a simple example ...

''assembler'' as a concept isnt hardware-specific, however the instructions used ARE hardware-specific.

The reason that code works on an AMD and an Intel chip is because both chips work to the same spec for instructions (x86).
However that code wont work on a Mac as it uses a different instruction set and the same with any other cpu which isnt "IBM compatible".
So, assembler code written for a PC wont work on a Mac, where as the C++ code will be compiled down to the native code for the platform you are compiling on.

As a side note bits of the assembler language are chip dependant, for example;
code using SSE instructions will fail on a P2 or a pre-XP AMD chip as they dont have those instuctions