Is that a way to declare a variable or it just a label (Nasm)?-CodePudding

As I know, when I want to reserve a memory (variable) I do the following:

msg db 'Hello world!',0
num db 10

But what about this:

str: db "Welcome to my OS", 0

My code (Very simple bootloader):

org 0x7c00
mov bp, 0x7c00
mov sp, bp 

mov ax, str
call printString

jmp $

printString:
    mov al, [str]
    mov ah, 0eh
    int 10h
  
str db 'W', 0 ; <-- str must to be str:

times 510-($-$$) db 0
dw 0xaa55

: is also used to declare variables or that is just a label?

because I use this way str: to reserve memory in bios mode.

CodePudding user response：

This is a rudiment of a MASM/TASM feature which doesn't exist in NASM. The rudiment is that you can leave out the colon after a label name when using certain directives.

In MASM/TASM there used to be a difference between placing the colon and not placing it, but no such difference exists in NASM.