Why can db accept more than 1 byte?

Question

If db stands for Define Byte and can hold 8 bits (1 byte), why can we use a 6 bytes string with db? I know that one character is only 1 byte, and db holds 1 byte.

section .data
    text db "Yellow"

db is playing like a char in more high level languages (compared to asm), which we can just increase the buffer, but assembly does it automatically?

#include <stdio.h>

int main(void)
{
    char c = 'Y';
    char string[7] = "Yellow";
    return 42;
}

You might be getting a compiler warning for `char c = "Y";` which should be `char c = 'Y';` — Weather Vane, Sep 05 '20 at 20:02
@ikegami I also thought like this, but look [here](https://stackoverflow.com/questions/10168743/which-variable-size-to-use-db-dw-dd-with-x86-assembly) — Pro Assembly Programmer, Sep 05 '20 at 20:03

fcdt · Accepted Answer · 2020-09-05T20:06:15.480

4

The data definitions db, dw, dd, dq etc. accept more than one value, they are stored successively. For example

db 'Y', 'e', 'l', 'l', 'o', 'w', 0

is assembled as

59 65 6C 6C 6F 77 00

Since it is cumbersome to specify all characters individually, there is the notation as a string, both are equivalent:

db "Yellow", 0

Please note that the terminating zero byte must be specified separately in assembly (in contrast to C).

edited Sep 05 '20 at 20:06

answered Sep 05 '20 at 20:04

fcdt

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It's even the same in C (except that C adds a NUL). `char s[] = "Yellow";` is short for `char s[] = { 'Y', 'e', 'l', 'l', 'o', 'w', 0 };` – ikegami Sep 05 '20 at 20:06
Cool! I didn't know. @ikegami – Pro Assembly Programmer Sep 05 '20 at 20:07

Why can db accept more than 1 byte?

1 Answers1