mov ecx,'hel' ;ECX=0x006c6568
mov edx,'l' ;EDX=0x0000006c
;...
mov eax,edx ;EAX=0x0000006c
shl eax,24 ;EAX=0x6c000000
or eax,ecx ;EAX=0x6c6c6568 = 'hell'    

mov ecx, 'hel'
mov edx, 'lo'
mov eax, edx
shl rax, 24
or rax, rcx    

One thing to realise is that the register EAX is 32-bits wide, so it can only hold a maximum of 4 bytes. So assuming you want just 4 bytes you can do this:

Code:

mov ecx,'hel' ;ECX=0x006c6568
mov edx,'l' ;EDX=0x0000006c
;...
mov eax,edx ;EAX=0x0000006c
shl eax,24 ;EAX=0x6c000000
or eax,ecx ;EAX=0x6c6c6568 = 'hell'    

buffer   db 'Hello', 0
buffer2 db ', World!', 0
buffer3 rb 100

.....

mov ecx, [buffer]
mov edx, [buffer2]
.....  ; something
mov [buffer3], eax

    

Thanks. But, for concatenate strings like this?

Code:

buffer   db 'Hello', 0
buffer2 db ', World!', 0
buffer3 rb 100

.....

mov ecx, [buffer]
mov edx, [buffer2]
.....  ; something
mov [buffer3], eax

    

;**************
;* Concat.asm *
;**************

format pe console 4.0
entry start

include 'win32a.inc'

section '.data' data readable writeable

    strPart1 db 'Hel',0
    strPart2 db 'lo.',0
    strFormat db '%s',13,10,0
    strResult rb 128

section '.code' code readable executable

    start:

        cinvoke strcpy,strResult,strPart1
        cinvoke strcat,strResult,strPart2
        cinvoke printf,strFormat,strResult
        invoke ExitProcess,0

section '.idata' import data readable writeable

  library kernel32,'kernel32.dll',\ 
          msvcrt,'msvcrt.dll' 

  import kernel32,\ 
         ExitProcess,'ExitProcess' 

  import msvcrt,\ 
         printf,'printf',\ 
         strcpy,'strcpy',\ 
         strcat,'strcat' 
    

NEASM wrote:

Thanks. But, for concatenate strings like this?

Code:

buffer   db 'Hello', 0
buffer2 db ', World!', 0
buffer3 rb 100

.....

mov ecx, [buffer]
mov edx, [buffer2]
.....  ; something
mov [buffer3], eax

    

First describe how would you store the resulting string in 4 bytes.

DimonSoft wrote:

First describe how would you store the resulting string in 4 bytes.

Excuse me, i'm not so expert.

Perhaps NEASM wants eax to hold the pointer to the resulting string, not the actual resulting string?!

(ie: ECX = "hel"; EDX = "lo"; EAX = "hello", for example)

Sorry for the trouble,

I've been looking for a long way to concatenate two strings and return their value to EAX (ie: ECX = "hel"; EDX = "lo"; EAX = "hello", for example), but I've never been able to find nothing about this. Could you give me a function in assembly that concatenates two strings? Thanks in advance.

EAX is 4 bytes.

'hel' is 3 bytes, but 'hello' is 5 bytes so it won't fit.

Furs wrote:

EAX is 4 bytes.

'hel' is 3 bytes, but 'hello' is 5 bytes so it won't fit.

We could try to use a different character set. A character set with 6 bits per character would allow 5 characters within 30 bits.

l = 00
e = 01
h = 10
o = 110
_ = 111
-------
14 bits    

l = 0
e = 100
h = 101
o = 110
_ = 111
-------
14 bits