Assembly Class Help

Xtreme Barton · Jan 14, 2013

this involves homework so I do not want the answer just posted up .. defeats the purpose of me learning

GOAL:

I need to read from a file into a buffer and display that buffer to the screen .. adjusting the buffer size to 1024 and use a loop to continue reading and writing till the file contains no more data..

the book gives me a program to start with and I need to modify it to the requirements ..

ORIGINAL

Code:

TITLE Reading a File                      (ReadFile.asm)

; Opens, reads, and displays a text file using
; procedures from Irvine32.lib. 

INCLUDE Irvine32.inc
INCLUDE macros.inc

BUFFER_SIZE = 50

.data
buffer BYTE BUFFER_SIZE DUP(?)
filename    BYTE 80 DUP(0)
fileHandle  HANDLE ?

.code
main PROC

; Let user input a filename.
    mWrite "Enter an input filename: "
    mov    edx,OFFSET filename
    mov    ecx,SIZEOF filename
    call    ReadString

; Open the file for input.
    mov    edx,OFFSET filename
    call    OpenInputFile
    mov    fileHandle,eax

; Check for errors.
    cmp    eax,INVALID_HANDLE_VALUE        ; error opening file?
    jne    file_ok                    ; no: skip
    mWrite <"Cannot open file",0dh,0ah>
    jmp    quit                        ; and quit
file_ok:

; Read the file into a buffer.
    mov    edx,OFFSET buffer
    mov    ecx,BUFFER_SIZE
    call    ReadFromFile
    jnc    check_buffer_size            ; error reading?
    mWrite "Error reading file. "        ; yes: show error message
    call    WriteWindowsMsg
    jmp    close_file
    
check_buffer_size:
    cmp    eax,BUFFER_SIZE            ; buffer large enough?
    jb    buf_size_ok                ; yes
    mWrite <"Error: Buffer too small for the file",0dh,0ah>
    jmp    quit                        ; and quit
    
buf_size_ok:    
    mov    buffer[eax],0        ; insert null terminator
    mWrite "File size: "
    call    WriteDec            ; display file size
    call    Crlf

; Display the buffer.
    mWrite <"Buffer:",0dh,0ah,0dh,0ah>
    mov    edx,OFFSET buffer    ; display the buffer
    call    WriteString
    call    Crlf

close_file:
    mov    eax,fileHandle
    call    CloseFile


quit:
    exit
main ENDP

END main

Xtreme Barton · Jan 15, 2013

so modifying the buffer seems ok step to take care of .. I guess now Im having an issue of how to call that while passing it the correct arguments ..

prototype is as follows ..

ReadFile Function Prototype

Code:

ReadFile Proto,
        hFile:HANDLE,                                          ; input handle
        lpBuffer:PTR BYTE,                                   ; ptr to buffer
        nNumberOfBytesToRead:DWORD               ; num bytes to read
        lpNumberOfBytesread:PTR DWORD,           ; byes actually read
        lpOverlapped:PTR DWORD                        ; ptr to asynch info

now why Im having a huge brain fart and dont know how to properly calll this is beyond me .. but I do know you call it multiple times and ReadFile will remember where it left off if say you chose to only use a very small "bytes to read argument" (nNumberOfBytesToRead)....

:bang head

Assembly Class Help

Xtreme Barton

Member

Xtreme Barton

Member

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