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Freiza
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 Posted: Wed Apr 11, 2012 12:21 pm Post subject: how to copy string |
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How to do this
Where is [ebx] is string[8]
I tried
mov byte ptr [ebx+0],'h'
mov byte ptr [ebx+1],'e'
mov byte ptr [ebx+2],'l'
mov byte ptr [ebx+3],'l'
mov byte ptr [ebx+4],'o'
mov byte ptr [ebx+5],0
but having problems also tried using hex values
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Kavvman
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Slugsnack
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| Posted: Wed Apr 11, 2012 6:05 pm Post subject: |
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| Kavvman wrote: | use the ascii code to store each letter. something like this
mov byte ptr [ebx], 43h
You can also use the rep instruction to perform string operations...read more here
http://faydoc.tripod.com/cpu/rep.htm |
The rep instruction is useless in this case since he is not copying a string. Copying byte by byte is also wasteful and will result in slow and redundantly verbose code. A DWORD can be copied instead.
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Dark Byte
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| Posted: Wed Apr 11, 2012 6:29 pm Post subject: |
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| Quote: |
mov byte ptr [ebx+0],'h'
mov byte ptr [ebx+1],'e'
mov byte ptr [ebx+2],'l'
mov byte ptr [ebx+3],'l'
mov byte ptr [ebx+4],'o'
mov byte ptr [ebx+5],0
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works fine. What is the problem ?
rep is also an option:
| Code: |
hellostr:
db 'hello',0
...
cld //clear the direction flag (else edi/esi might go backwards)
mov edi,ebx //set destination
mov esi,teststr //set origin
mov ecx,6 //set number of bytes to copy
rep movsb //repeat movsb ecx times
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Kavvman
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| Posted: Wed Apr 11, 2012 6:46 pm Post subject: |
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| Slugsnack wrote: | | Kavvman wrote: | use the ascii code to store each letter. something like this
mov byte ptr [ebx], 43h
You can also use the rep instruction to perform string operations...read more here
http://faydoc.tripod.com/cpu/rep.htm |
The rep instruction is useless in this case since he is not copying a string. Copying byte by byte is also wasteful and will result in slow and redundantly verbose code. A DWORD can be copied instead. |
Keep your crap existence to the useless section.
The OP had trouble with strings operation, his thread title is "how to copy string". A helpful reply would be to show the different ways he can solve the problem and if he is copying a string the reps instruction is the best he can use. The thread isn't about performance anyway.
@DB: small correction
| Quote: | hellostr:
db 'hello',0
...
cld //clear the direction flag (else edi/esi might go backwards)
mov edi,ebx //set destination
mov esi,teststr //set origin :> should be hellostr
mov ecx,6 //set number of bytes to copy
rep movsb //repeat movsb ecx times |
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Freiza
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| Posted: Wed Apr 11, 2012 6:57 pm Post subject: |
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| Dark Byte wrote: | | Quote: |
mov byte ptr [ebx+0],'h'
mov byte ptr [ebx+1],'e'
mov byte ptr [ebx+2],'l'
mov byte ptr [ebx+3],'l'
mov byte ptr [ebx+4],'o'
mov byte ptr [ebx+5],0
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works fine. What is the problem ?
rep is also an option:
| Code: |
hellostr:
db 'hello',0
...
cld //clear the direction flag (else edi/esi might go backwards)
mov edi,ebx //set destination
mov esi,teststr //set origin
mov ecx,6 //set number of bytes to copy
rep movsb //repeat movsb ecx times
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yes that was not the problem. I messed up the pointers and you helped me out.
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