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Nov 6th, 2009
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int 21h/ah=09h string output

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im using fasm (flat assembler 1.68), and im trying to output a string with int21h/ah=09h

Assembly Syntax (Toggle Plain Text)
  1. jmp main
  2. msg db "hello world$"
  3. main:
  4. mov dx, msg
  5. mov ah, 09
  6. int 21h

this code outputs "hello world", but it outputs some control characters before it ([SOME WEIRD CONTROL CHARACTERS]hello world)

so how can i fix this?
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brando|away is offline Offline
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Nov 6th, 2009
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Re: int 21h/ah=09h string output
Strange.

Presumably DOS, or you'd get nothing.

I notice the lack of a return statement. The control chars may appear at the beginning of the line, but that doesn't mean they were printed before your message. You might be running past the end of your program, and hitting something that moves the cursor, then prints who-knows-what.

Also, I don't see any segment setup, so this is a com program?
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dan63043 is offline Offline
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Re: int 21h/ah=09h string output
Click to Expand / Collapse  Quote originally posted by dan63043 ...
Strange.

Presumably DOS, or you'd get nothing.

I notice the lack of a return statement. The control chars may appear at the beginning of the line, but that doesn't mean they were printed before your message. You might be running past the end of your program, and hitting something that moves the cursor, then prints who-knows-what.

Also, I don't see any segment setup, so this is a com program?
yes its DOS, and yes its a com program. And that was only part of the program.

even if i put
Assembly Syntax (Toggle Plain Text)
  1. mov ah, 4Ch
  2. int 21h
or 'ret'

i still see control characters before my message
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brando|away is offline Offline
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Nov 7th, 2009
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Re: int 21h/ah=09h string output
Hmmm... not a fasm user, so just some other observations. No org statement, or use 16 statement. Thought fasm syntax was a dollar symbol before hex numbers, but that may be optional. Some assemblers need exe2bin to fix linkage of programs. Maybe give us the whole program and the process you follow and it could attract a solution.

Actually, it's so short, a dir listing of executable (so we see file size) and use debug to dump the contents, and post it here.
Last edited by dan63043; Nov 7th, 2009 at 2:54 am. Reason: Add request for debug output
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Re: int 21h/ah=09h string output
Click to Expand / Collapse  Quote originally posted by dan63043 ...
Hmmm... not a fasm user, so just some other observations. No org statement, or use 16 statement. Thought fasm syntax was a dollar symbol before hex numbers, but that may be optional. Some assemblers need exe2bin to fix linkage of programs. Maybe give us the whole program and the process you follow and it could attract a solution.

Actually, it's so short, a dir listing of executable (so we see file size) and use debug to dump the contents, and post it here.
Heres the disassembly:

Assembly Syntax (Toggle Plain Text)
  1. 1462:0100 EB0C          JMP     010E
  2. 1462:0102 68            DB      68
  3. 1462:0103 65            DB      65
  4. 1462:0104 6C            DB      6C
  5. 1462:0105 6C            DB      6C
  6. 1462:0106 6F            DB      6F
  7. 1462:0107 20776F        AND     [BX+6F],DH
  8. 1462:010A 726C          JB      0178
  9. 1462:010C 64            DB      64
  10. 1462:010D 24BA          AND     AL,BA
  11. 1462:010F 0200          ADD     AL,[BX+SI]
  12. 1462:0111 B409          MOV     AH,09
  13. 1462:0113 CD21          INT     21
  14. 1462:0115 B44C          MOV     AH,4C
  15. 1462:0117 CD21          INT     21
  16. 1462:0119 0200          ADD     AL,[BX+SI]
  17. 1462:011B B409          MOV     AH,09
  18. 1462:011D CD21          INT     21
  19. 1462:011F B44C          MOV     AH,4C
  20. -u
  21. 1462:0121 CD21          INT     21
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brando|away is offline Offline
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Re: int 21h/ah=09h string output
Ha! Isn't funny how we overlook the obvious? When you pointed DX at 0002, you forgot that your program actually loads at 0100. Just change
Assembly Syntax (Toggle Plain Text)
  1. MOV     DX,0002
to
Assembly Syntax (Toggle Plain Text)
  1. MOV     DX,0102

BTW, here's how to use debug to get a decent listing (ok, pathetic listing, but we're using "debug")

Assembly Syntax (Toggle Plain Text)
  1. -u100,101
  2. 139A:0100 EB0C          JMP     010E
  3. -d102,10d
  4. 139A:0100        68 65 6C 6C 6F 20-77 6F 72 6C 64 24           hello world$
  5. -u10e,122
  6. 139A:010E BA0200        MOV     DX,0002
  7. 139A:0111 B409          MOV     AH,09
  8. 139A:0113 CD21          INT     21
  9. 139A:0115 B44C          MOV     AH,4C
  10. 139A:0117 CD21          INT     21
  11. 139A:0119 0200          ADD     AL,[BX+SI]
  12. 139A:011B B409          MOV     AH,09
  13. 139A:011D CD21          INT     21
  14. 139A:011F B44C          MOV     AH,4C
  15. 139A:0121 CD21          INT     21
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dan63043 is offline Offline
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Nov 8th, 2009
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Re: int 21h/ah=09h string output
thanks, turns out i should of had an org statement in the first place
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brando|away is offline Offline
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Jun 18th, 2010
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Re: int 21h/ah=09h string output
need code snake game
run emu8086
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skyir is offline Offline
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Nov 7th, 2010
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Re: int 21h/ah=09h string output
Hi, I'm trying to print the $ character. I tried putting a "\" but it didnt work..
Any idea??
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davibq is offline Offline
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