Chapter 6: Input and Output Operations in MASM

Introduction:

Importance of input and output operations in assembly language programming

Overview of input and output methods available in MASM

Console Input and Output:

Reading user input from the console using interrupt 21h

Displaying output to the console using interrupt 21h

Handling string input and output operations

File Input and Output:

Opening, reading, writing, and closing files in MASM

Using interrupts 21h and 3Dh for file input/output operations

Handling text files and binary files in MASM

Example:

assembly

Copy code

.model small

.stack 100h

.data

    prompt db 'Enter your name: $'

    name db 50 dup(0)

    filename db 'data.txt', 0

    buffer db 50 dup(0)

.code

main proc

    mov ax, @data

    mov ds, ax

    ; Console input

    lea dx, prompt

    mov ah, 9

    int 21h

    lea dx, name

    mov ah, 0Ah

    int 21h

    ; Console output

    lea dx, name

    mov ah, 9

    int 21h

    ; File output

    mov ah, 3Ch ; create or open file

    lea dx, filename

    mov cx, 0 ; file attributes (normal)

    int 21h

    mov bx, ax ; save file handle

    lea dx, name

    mov cx, 50 ; number of bytes to write

    mov ah, 40h ; write to file

    int 21h

    ; File input

    mov ah, 3Dh ; open existing file

    lea dx, filename

    int 21h

    mov bx, ax ; save file handle

    lea dx, buffer

    mov cx, 50 ; number of bytes to read

    mov ah, 3Fh ; read from file

    int 21h

    ; Display file content

    lea dx, buffer

    mov ah, 9

    int 21h

    ; Close file

    mov ah, 3Eh ; close file

    mov bx, ax ; file handle

    int 21h

    mov ah, 4Ch

    int 21h

main endp

end main

In this example, we demonstrate input and output operations in MASM. We have a prompt message, prompt, a name buffer, name, a filename, filename, and a general-purpose buffer, buffer.

For console input, we use the DOS interrupt 21h with function 0Ah. We display the prompt message using the ah register set to 9, and then read the user's input into the name buffer.

For console output, we display the contents of the name buffer using the DOS interrupt 21h with function 9.

For file output, we create or open a file named data.txt using the DOS interrupt 21h with function 3Ch. We write the contents of the name buffer to the file using the DOS interrupt 21h with function 40h.

For file input, we open an existing file using the DOS interrupt 21h with function 3Dh. We read the contents of the file into the buffer using the DOS interrupt 21h with function 3Fh.

Finally, we display the contents of the buffer using the DOS interrupt 21h with function 9.

By understanding input and output operations in MASM, readers can interact with users through console input and output, as well as read from and write to files. They learn how to use interrupt 21h to handle console input and output, as well as file input and output operations. This knowledge enables them to build interactive programs and work with external data sources in their assembly language programs.