Index
> DOS > Opening file and going throught it byte by byte. |
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freecrac 13 May 2014, 07:58
Hello.
With the read function it is possible to load 64 KB bytes into our buffer and with a following read we can load the next 64 KB of the file and so on. In the AX-register we get the number of bytes actually read. RBIL->inter61b.zip->INTERRUP.F Quote:
But it is also possible to get the length of the file before loading. Quote:
Code: mov ah, 42h mov bx, [HANDLE] mov al, 2 ; from the end of file mov cx, 0 ; high mov dx, 0 ; low int 21h mov [LENGTH_LOW], ax mov [LENGTH_HIGH], dx mov ah, 42h ; set the file pointer to the start position mov bx, [HANDLE] mov al, 0 ; start of file mov cx, 0 ; high mov dx, 0 ; low int 21h Dirk |
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13 May 2014, 07:58 |
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mmajewski 13 May 2014, 08:54
I have written this code (using your code example):
Code: mov dx, FileNameToFind mov al, 2 ;access mode - read and write mov ah, 03Dh ;function 3Dh -open a file int 21h jc ErrorOpening ;if carry flag is set jump to ErrorOpening mov [FileHandle], ax ;saving file handle mov ah, 42h mov bx, [FileHandle] mov al, 2 ;from the end of file mov cx, 0 ;high mov dx, 0 ;low int 21h mov [LENGTH_LOW], ax mov [LENGTH_HIGH], dx mov ah, 42h ;set the file pointer mov bx, [FileHandle] mov al, 0 mov cx, 0 mov dx, 0 int 21h FileHandle dw 0 LENGTH_HIGH dw 0 LENGTH_LOW dw 0 I do not understand this code quite a bit. Why are you doing this Code: mov ah, 42h ;set the file pointer mov bx, [FileHandle] mov al, 0 mov cx, 0 mov dx, 0 int 21h after it is clear what is the size of file? Should the function to read the file be like?: Code: mov ah, 3Fh mov bx, [FileHandle] mov cx, [LENGTH_HIGH] mov dx, buff int 21h It actually is not working, I did not know why. Still I have no clue how to access data from file, for example how to print it. Could you elaborate on this more, please? |
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13 May 2014, 08:54 |
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freecrac 13 May 2014, 10:39
After we get the length of the file by setting the file pointer to the end of the file, we have to set the file pointer back to the start position, because the read function will read beginning at current file position.
And the number of bytes for to read can only have a maximal size of 0FFFFh bytes and if the file size is greater, then we have to read again by calling the read funtion again. Each reading will additional move the file pointer forward, so the next read will be continue at current file position. This "mov cx, [LENGTH_HIGH]" is wrong because this contains only the high word of the file length, but we can only read 0FFFFh of bytes with calling the read function. Example if the file size is greater than 0FFFFh, then the highword of the file length contains a value greater 0, but otherwise it contains 0. For to read we can put a value of 0FFFFh in CX for to load the first part of the file. And then we can read again the next parts with calling the read function again with CX=0FFFFh. The read function return in AX the number of bytes actually read or a 0 value, if we get the end of the file before calling. The access of the bytes of the file is similar with the access of any data in the ram. For printing the (ASCII-) bytes to the screen we can use function 0Eh of the int 10h. RBIL->inter61a.zip->INTERRUP.A Quote: --------b-100E--CXABCD----------------------- But if the bytes do not have an ASCII character, then we can print the number of the bytes instead. For a decimal output we have to split the value in different ASCII numbers by dividing the number with 100 and with 10, beginning with the highest part of the number and to convert it to ASCII with adding "0" to each value printing from the left to the rigth side of the number. For a hexadecimal output we have to seperate each half nibble of the byte also beginning with the highest part of the number. Then checking if the value is greater 9 and if it is, then we have to add a 7 to it for to get the letter from A-F and additional with adding "0" to the value for to convert it to ASCII. Dirk |
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13 May 2014, 10:39 |
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mmajewski 15 May 2014, 19:00
Thank you! It helped me a lot !
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15 May 2014, 19:00 |
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henry.37 28 Mar 2015, 16:03
Hello, I am having a hard time trying to print the file smaller than 128 kB. I am an assembly noob, so it´s hard to understand everything. How would you do it ?
freecrac wrote: Hello. |
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28 Mar 2015, 16:03 |
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baldr 28 Mar 2015, 18:44
henry.37,
Can you be more specific about the problem you've trouble with? Open file with int21/3D, read a chunk of it into a buffer with int21/3F, output read chunk with int21/40, repeat until EOF. Don't forget to close file with int21/3E afterwards (just to behave nicely). Error checking is a good thing too. |
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28 Mar 2015, 18:44 |
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henry.37 28 Mar 2015, 20:24
i´ve opened file, but here comes to problem, i am disoriented with spliting the file, [LENGTH_LOW] / [LENGTH_HIGH] should be size of buffer, so i should create buffer with size [LENGTH_LOW/high] and throw it to buffer, than simply print it. Opening and closing are working fine, I checked it. Sorry if the code is terrible, i'm not good at it.
This is my procedure: read_print_FILE PROC mov ax,4200h ;read mov bx,filehandle ;file handle mov al,0 mov cx,1 ;file pointer to cx mov dx,1 ;file pointer to dx int 21h ;vykonaj jc ERROR mov [LENGTH_LOW], ax ;velkost nacitana mov [LENGTH_HIGH], dx mov cx,LENGTH_LOW ; size to print lower mov dx,offset buff int 21h vypis buff ;macro to print mov cx,LENGTH_HIGH ; size to print higher mov dx,offset buff int 21h vypis buff ;macro to print mov ah, 42h ; set the file pointer to the start position mov bx, filehandle mov al, 0 ; start of file mov cx, 0 ; high mov dx, 0 ; low int 21h jc ERROR ; je N_chybaC jmp N_koniecPC ERROR: vypis chybstC ;print "problem handling the file" N_koniecPC: ret ENDP ;macro to print vypis MACRO tx xor ax,ax mov ah,9 ;9 vezme cely retazec, nie len 1 bit az po dolar, do ah mov dx,offset tx ;do dx je potrebne dat offset aby mohlo textu1 int 21h ENDM ;aand bsize EQU 32768 buff DB bsize dup ('$') filehandle DW 0 baldr wrote: henry.37, |
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28 Mar 2015, 20:24 |
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AsmGuru62 29 Mar 2015, 01:57
Is this what you want?
Code:
; ---------------------------------------------------------------------------
; FILE: DosType.Asm
; DATE: March 28, 2015
; ---------------------------------------------------------------------------
;
; COM file standard header
;
org 100h
use16
;
; MS-DOS Program Entry Point
;
mov dx, TextBuffer
call TeletypeTheFile
;
; Quit to MS-DOS
;
int 20h
;
; Procedure to load file by pieces and print it on console
;
TeletypeTheFile:
; --------------------------------------------------------
; INPUT:
; DS:DX = file name
; --------------------------------------------------------
;
; Open file
;
mov ax, 3D00h
int 21h
jc .no_file
;
; File opened - store handle into variable
;
mov [HFile], ax
;
; Read 511 bytes into 'TextBuffer'
;
.read_more:
mov bx, [HFile]
mov cx, 511
mov dx, TextBuffer
mov ah, 3Fh
int 21h
jc .read_error
;
; Check if anything is loaded from file (# of loaded bytes is in AX)
;
test ax, ax
jz .no_more_bytes
;
; Terminate loaded text with '$'
;
mov si, dx
add si, ax
mov byte [si], '$'
;
; Print piece to console and continue loading until no bytes left
;
mov ah, 9
int 21h
jmp .read_more
.no_more_bytes:
;
; Close the file
;
mov bx, [HFile]
mov ah, 3Eh
int 21h
ret
.read_error:
mov ah, 9
mov dx, CantRead
int 21h
.no_file:
mov ah, 9
mov dx, NoSuchFile
int 21h
ret
;
; Data section
;
HFile dw 0
NoSuchFile db 0Dh,0Ah,'File Not Found.',0Dh,0Ah,'$'
CantRead db 0Dh,0Ah,'Cannot Read This File.',0Dh,0Ah,'$'
FileName db 'C:\Tools\FASM\SOURCE\IDE\FASMW\FASMW.ASM',0 ; <-- put here your file name
TextBuffer rb 512
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29 Mar 2015, 01:57 |
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henry.37 29 Mar 2015, 11:19
This does quite lots of error hard to fix,
*TextBuffer rb 512 - (textbuffer undefined, should be here dw ?,db is out of range) *mov byte [si], '$' -(argument needs type override) *mov dx, CantRead -(operand type do not match, i guess you forgot offset CantRead) *mov dx, NoSuchFile -(same as above) After trying to fix errors as i suggested above, it gives me ERROR with *mov byte [si], '$' AsmGuru62 wrote: Is this what you want? |
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29 Mar 2015, 11:19 |
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henry.37 29 Mar 2015, 11:26
also, shouldnt be there procedure to call actuall read ? there is open, but shouldnt be there after that "mov ah,3fh" to read ?
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29 Mar 2015, 11:26 |
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revolution 29 Mar 2015, 11:26
henry.37 wrote: This does quite lots of error hard to fix, |
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29 Mar 2015, 11:26 |
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henry.37 29 Mar 2015, 11:31
no, i am using Tasm, for school study purpose.
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29 Mar 2015, 11:31 |
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AsmGuru62 29 Mar 2015, 17:46
I see.
There are only few places where TASM code would be different from FASM. Like when you need an address of a variable you use OFFSET in TASM. Code: mov si, Buffer ; FASM mov si, OFFSET Buffer ; TASM If you want to load a value from memory, remove brackets: Code: mov bx, [HFile] ; FASM mov bx, HFile ; TASM The directive 'rb' I used to reserve buffer is probably also different - something with DUP... I forgot TASM already, so you'll have to translate the code using some TASM manuals. You should have those since you are studying TASM in school. Also, you can read the logic of the code and do the same in TASM. I think the code logic is what matters in your question. |
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29 Mar 2015, 17:46 |
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revolution 30 Mar 2015, 09:36
AsmGuru62 wrote: If you want to load a value from memory, remove brackets: |
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30 Mar 2015, 09:36 |
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DOS386 02 Apr 2015, 17:59
henry.37 wrote: no, i am using Tasm, for school study purpose. Damn. Please tell your teacher about FASM. > With the read function it is possible to load 64 KB bytes into our buffer NOT true. Unfortunately we can read up to $FFFF AKA 65'535 AKA (64 Ki - 1) Octet's only. So if we want to read a big file, what block size to use? $FFFF ? $FFFE ? $FFFC ? $FFF0 ? $FF00 ? $FE00 ? $F000 ? $C000 ? $8000 ? The dilemma is not solvable ($FE00 seems to give good performance). > In Ideal mode: the brackets are mandatory. YES, TASM has an "ideal mode", and it's more similar to FASM. And YES, FASM design is partly inspired by TASM ideal mode. > (Random worlds separated by "Space") Be prepared to encounter other junk. > I do not know the size of file but I assume there are not > any worlds in English that consists >30 letters. This is a dangerous approach. > So I declared: > ToFind0 db 30 dup(0) > ToFind1 db 30 dup(0) > ToFind2 db 30 dup(0) > I want my program to store 'RandomWorld1$" under > ToFind0, 'RandomWorld2$' under ToFind1 and so on.. This is desperately inefficient. What are you trying to do ? Just count words ? This is very simple if your file is < 64 KiO, if it's above, it's more tricky, as your buffer border may fall between 2 words, or into a word. Hist: try to count words in a file < 64 KiO for the start. _________________ Bug Nr.: 12345 Title: Hello World program compiles to 100 KB !!! Status: Closed: NOT a Bug |
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02 Apr 2015, 17:59 |
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