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Table of Content | Chapter Thirteen (Part 8) |
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Table of Content | Chapter Thirteen (Part 8) |
| CHAPTER THIRTEEN: MS-DOS PC-BIOS AND FILE I/O (Part 7) |
| 13.3.9 -
File I/O Examples 13.3.9.1 - Example #1: A Hex Dump Utility 13.3.9.2 - Example #2: Upper Case Conversion |
Of course one of the main reasons for making calls to DOS is to manipulate files on a mass storage device. The following examples demonstrate some uses of character I/O using DOS.
13.3.9.1 Example #1: A Hex Dump Utility
This program dumps a file in hexadecimal format. The filename must be hard coded into the file (see "Accessing Command Line Parameters" later in this chapter).
include stdlib.a includelib stdlib.lib cseg segment byte public 'CODE' assume cs:cseg ds:dseg es:dseg ss:sseg ; Note CR and LF are already defined in STDLIB.A tab equ 09h MainPgm proc far ; Properly set up the segment registers: mov ax seg dseg mov es ax ;Leave DS pointing at PSP ;--------------------------------------------------------------- ; ; First parse the command line to get the filename: mov si 81h ;Pointer to command line lea di FileName ;Pointer to FileName buffer SkipDelimiters: lodsb ;Get next character call TestDelimiter je SkipDelimiters ; Assume that what follows is an actual filename dec si ;Point at 1st char of name GetFName: lodsb cmp al 0dh je GotName call TestDelimiter je GotName stosb ;Save character in file name jmp GetFName ; We're at the end of the filename so zero-terminate it as ; required by DOS. GotName: mov byte ptr es:[di] 0 mov ax es ;Point DS at DSEG mov ds ax ; Now process the file mov ah 3dh mov al 0 ;Open file for reading lea dx Filename ;File to open int 21h jnc GoodOpen print byte 'Cannot open file aborting program...' cr 0 jmp PgmExit GoodOpen: mov FileHandle ax ;Save file handle mov Position 0 ;Initialize file position ReadFileLp: mov al byte ptr Position and al 0Fh ;Compute (Position MOD 16) jnz NotNewLn ;Every 16 bytes start a line putcr mov ax Position ;Print offset into file xchg al ah puth xchg al ah puth print byte ': ' 0 NotNewLn: inc Position ;Increment character count mov bx FileHandle mov cx 1 ;Read one byte lea dx buffer ;Place to store that byte mov ah 3Fh ;Read operation int 21h jc BadRead cmp ax 1 ;Reached EOF? jnz AtEOF mov al Buffer ;Get the character read and puth ; print it in hex mov al ' ' ;Print a space between values putc jmp ReadFileLp BadRead: print byte cr lf byte 'Error reading data from file aborting.' byte cr lf 0 AtEOF: mov bx FileHandle ;Close the file mov ah 3Eh int 21h ;--------------------------------------------------------------- PgmExit: ExitPgm MainPgm endp TestDelimiter proc near cmp al ' ' je xit cmp al ' ' je xit cmp al Tab je xit cmp al ';' je xit cmp al '=' xit: ret TestDelimiter endp cseg ends dseg segment byte public 'data' PSP word ? Filename byte 64 dup (0) ;Filename to dump FileHandle word ? Buffer byte ? Position word 0 dseg ends sseg segment byte stack 'stack' stk word 0ffh dup (?) sseg ends zzzzzzseg segment para public 'zzzzzz' LastBytes byte 16 dup (?) zzzzzzseg ends end MainPgm
13.3.9.2 Example #2: Upper Case Conversion
The following program reads one file converts all the lower case characters to upper case and writes the data to a second output file.
include stdlib.a includelib stdlib.lib cseg segment byte public 'CODE' assume cs:cseg ds:dseg es:dseg ss:sseg MainPgm proc far ; Properly set up the segment registers: mov ax seg dseg mov ds ax mov es ax ;---------------------------------------------------------------- ; ; Convert UCCONVRT.ASM to uppercase ; ; Open input file: mov ah 3dh mov al 0 ;Open file for reading lea dx Filename ;File to open int 21h jnc GoodOpen print byte 'Cannot open file aborting program...' cr lf 0 jmp PgmExit GoodOpen: mov FileHandle1 ax ;Save input file handle ; Open output file: mov ah 3Ch ;Create file call mov cx 0 ;Normal file attributes lea dx OutFileName ;File to open int 21h jnc GoodOpen2 print byte 'Cannot open output file aborting program...' byte cr lf 0 mov ah 3eh ;Close input file mov bx FileHandle1 int 21h jmp PgmExit ;Ignore any error. GoodOpen2: mov FileHandle2 ax ;Save output file handle ReadFileLp: mov bx FileHandle1 mov cx 1 ;Read one byte lea dx buffer ;Place to store that byte mov ah 3Fh ;Read operation int 21h jc BadRead cmp ax 1 ;Reached EOF? jz ReadOK jmp AtEOF ReadOK: mov al Buffer ;Get the character read and cmp al 'a' ; convert it to upper case jb NotLower cmp al 'z' ja NotLower and al 5fh ;Set Bit #5 to zero. NotLower: mov Buffer al ; Now write the data to the output file mov bx FileHandle2 mov cx 1 ;Read one byte lea dx buffer ;Place to store that byte mov ah 40h ;Write operation int 21h jc BadWrite cmp ax 1 ;Make sure disk isn't full jz ReadFileLp BadWrite: print byte cr lf byte 'Error writing data to file aborting operation' byte cr lf 0 jmp short AtEOF BadRead: print byte cr lf byte 'Error reading data from file aborting ' byte 'operation' cr lf 0 AtEOF: mov bx FileHandle1 ;Close the file mov ah 3Eh int 21h mov bx FileHandle2 mov ah 3eh int 21h ;---------------------------------------------------------------- PgmExit: ExitPgm MainPgm endp cseg ends dseg segment byte public 'data' Filename byte 'ucconvrt.asm' 0 ;Filename to convert OutFileName byte 'output.txt' 0 ;Output filename FileHandle1 word ? FileHandle2 word ? Buffer byte ? Position word 0 dseg ends sseg segment byte stack 'stack' stk word 0ffh dup (?) sseg ends zzzzzzseg segment para public 'zzzzzz' LastBytes byte 16 dup (?) zzzzzzseg ends end MainPgm
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Table of Content | Chapter Thirteen (Part 8) |
Chapter Thirteen: MS-DOS
PC-BIOS and
File I/O (Part 7)
28 SEP 1996
