classReader.asm

URL: https://mirkwood.cs.edinboro.edu/~bennett/class/cmsc3100/spring2026/notes/files/code/classReader.asm

 
%include "CONSTANTS.h"

    ; linux/unix definintions
    ; see main open for more info
    SYS_OPEN equ 2
    SYS_CLOSE equ 3
    O_RDONLY equ 0

section .data
    ;fileName: db `afile`,0
    fileName: db `ocap.txt`,0

    fd: dq 0  ; the file descriptor

    stringFMT: db `"%s"\n`,0

section .bss
    newWord resb 101

section .text

global main
main:
 
    ; open the file
    mov rax, SYS_OPEN
    mov rdi, fileName
    mov rsi, O_RDONLY
    mov rdx, 0
    syscall

    ; save the file descriptor
    mov [fd], rax
  
    ; read at most 100 bytes from the fiel
    mov rax, SYS_READ
    mov rdi, [fd]
    mov rsi, newWord
    mov rdx, 100
    syscall

    ; rax will contain the number of bytes read
    mov byte [newWord + rax], 0

    ; print out the string we just got
    mov rdi, stringFMT
    mov rsi, newWord
    call CallPrintf

    ; close the file
    mov  rax, SYS_CLOSE
    mov rdi, [fd]
    syscall

    jmp Exit