CODEWITHSUNDEEP
assemblyconsoledosnasm
Jason Baker
Jason Baker

Reputation: 198657

dollar-terminated strings

In my assembly language class, our first assignment was to write a program to print out a simple dollar-terminated string in DOS. It looked something like this:

BITS 32
    global _main

section .data
    msg db "Hello, world!", 13, 10, ’$’

section .text
_main:
mov ah, 9
mov edx, msg
int 21h
ret

As I understand it, the $ sign serves to terminate the sting like null does in C. But what do I do if I want to put a dollar sign in the string (like I want to print out "it costs $30")? This seems like a simple question, but my professor didn't know the answer and I don't seem to find it using a google search.

Upvotes: 4

Views: 5768

Answers (7)

Martin Rosenau
Martin Rosenau

Reputation: 18513

I prefer using the write service (AH=0x40):

  • AH=0x40
  • BX is the file handle; use the value 1 to write to the same device (such as the screen) as service AH=9
  • CX is the number of bytes to be written; the data is not "terminated" (neither by NUL nor by $), so all values (from 0 to 255) can be written
  • DS:DX points to the data (in your case: the string) to be written
    (Just like for service AH=9; If you use a 32-bit DOS extension: EDX, of course)

The service is actually intended for writing data to a file; however, it can also be used to write a "string" to the "output" by setting BX to 1.

Upvotes: 3

Adnan Chaudhary
Adnan Chaudhary

Reputation: 1

You can use 02 service of INT 21H instead of 09 service.

Here is the sample.

mov dl, '$'

mov ah,02

int 21h

Upvotes: -1

codelogic
codelogic

Reputation: 73672

You can't use DOS's 0x09 service to display $ signs, you'll need to use 0x02. See here.

Upvotes: 9

gbarry
gbarry

Reputation: 10554

One way is to find the call that prints a single character. You can print any character with that. Break the string up and print "it costs ", then the '$', and finally, "30". More work, but it gets the job done.

Upvotes: 0

Jonas Engström
Jonas Engström

Reputation: 5065

Or make your own print_string to print a NULL-terminated string using the undocumented INT 29h (print character in AL).

; ds:si = address of string to print
print_string:
    lodsb                   ; load next character from ds:si
    or al, al               ; test for NULL-character
    jz .end_of_string       ; end of string encountered, return.
    int 29h                 ; print character in AL on screen
    jmp print_string        ; print next character
.end_of_string:
    ret                     ; return to callers cs:ip

(Assuming you are using NASM)

Upvotes: 3

Jacek Ławrynowicz
Jacek Ławrynowicz

Reputation: 2700

Try '$$', '\044' (octal) or '\x24' (hex)

Upvotes: -5

Calyth
Calyth

Reputation: 1673

Um. You could write assembly that would taken into account for escaped $, e.g. \$? But then your \ becomes a special symbol too, and you need to use \\ to print a \

Upvotes: -2

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