Copy a string: Difference between revisions
→{{header|8086 Assembly}}
Puppydrum64 (talk | contribs) |
Puppydrum64 (talk | contribs) |
||
Line 63:
Terminated: ;the null terminator is already stored along with the string itself, so we are done.
;program ends here.</lang>
=={{header|8086 Assembly}}==
The technique varies depending on whether you just want a new reference to the old string or to actually duplicate it in RAM. Strangely, this is one of the few things that's actually easier to do correctly in assembly than in high-level languages - it's very unlikely you'll do the wrong one by accident.
===Making a new reference===
This technique is useful if you wish to create a struct/record that needs to be able to retrieve a string quickly. All you need to do is get a pointer to the desired string and store it in RAM.
<lang asm>.model small
.stack 1024
.data
myString byte "Hello World!",0 ; a null-terminated string
myStruct word 0
.code
mov ax,@data
mov ds,ax ;load data segment into DS
mov bx,offset myString ;get the pointer to myString
mov word ptr [ds:myStruct],bx
mov ax,4C00h
int 21h ;quit program and return to DOS</lang>
===Creating a "deep copy"===
This method will actually make a byte-for-byte copy somewhere else in RAM.
<lang asm>.model small
.stack 1024
.data
myString byte "Hello World!",0 ; a null-terminated string
StringRam byte 256 dup (0) ;256 null bytes
.code
mov ax,@data
mov ds,ax ;load data segment into DS
mov es,ax ;also load it into ES
mov si,offset myString
mov di,offset StringRam
mov cx,12 ;length of myString
cld ;make MOVSB auto-increment rather than auto-decrement (I'm pretty sure DOS begins with
;the direction flag cleared but just to be safe)
rep movsb ;copies 12 bytes from [ds:si] to [es:di]
mov al,0 ;create a null terminator
stosb ;store at the end. (It's already there since we initialized StringRam to zeroes, but you may need to do this depending
;on what was previously stored in StringRam, if you've copied a string there already.
mov ax,4C00h
int 21h ;quit program and return to DOS</lang>
=={{header|AArch64 Assembly}}==
| |||