Null character is not acting as end of string in assembly (NASM)

Question

In c language we can use '\0' null character as end of string.

#include <stdio.h>
int main() {
    char msg[] = "hello\0world";
    printf("msg = %s", msg);
}

This code will print just hello . Not world.

But In linux x86 NASM I'm using the following code but it is printing helloworld .

section .data
msg db "hello", 0, "world"

section .text
global main
main:
    mov eax, 4
    mov ebx, 1
    mov ecx, msg
    mov edx, 20
    int 0x80

    mov eax, 1
    mov ebx, 0
    int 0x80
    ret

Why null character is not working here as end of string? And what can I do to get that in assembly?

Answer 1

You use the write system call to write the data with the exact size you specify. The write function have no knowledge of the data it writes, it's just a series of bytes.

If you want to write a null-terminated string, you either need to find the position of the terminator and calculate the length from that position, or use a function that knows about C null-terminated strings.