How do I test to ensure only an integer is entered and ensure length of input is 5 bytes or less in the following code?
I am trying to understand how to properly control input so that the input beyond 5 bytes is not outputted to the terminal upon exiting of the program.
In addition, how would I test to ensure only a string is entered and finally in the last scenario, only a double is entered?
*** Updated code based on x82 and Peter C's guidance. I did some C disas and was able to amend my original code below. It still has some flaws but you are both a great deal of help! I am just stuck on when more than 5 integer bytes are entered it wont re-prompt as it does when I enter in a character data as it continues to dump extra bytes data to tty.
SECTION .data ; initialized data section
promptInput db 'Enter Number: ', 0
lenPromptInput equ $ - promptInput
displayInput db 'Data Entered: ', 0
lenDisplayInput equ $ - lenDisplayInput
SECTION .bss ; uninitialized data section
number resb 1024 ; allocate 1024 bytes for number variable
SECTION .text ; code section
global _start ; linker entry point
_start:
nop ; used for debugging
Read:
mov eax, 4 ; specify sys_write call
mov ebx, 1 ; specify stdout file descriptor
mov ecx, promptInput ; display promptInput
mov edx, lenPromptInput ; length of promptInput
int 0x80 ; call sys_write
mov eax, 3 ; specify sys_read call
mov ebx, 0 ; specify stdin file descriptor
mov ecx, number ; pass address of the buffer to read to
mov edx, 1024 ; specify sys_read to read 1024 bytes stdin
int 0x80 ; call sys_read
cmp eax, 0 ; examine sys_read return value in eax
je Exit ; je if end of file
cmp byte [number], 0x30 ; test input against numeric 0
jb Read ; jb if below 0 in ASCII chart
cmp byte [number], 0x39 ; test input against numeric 9
ja Read ; ja if above 9 in ASCII chart
Write:
mov eax, 4 ; specify sys_write call
mov ebx, 1 ; specify stdout file descriptor
mov ecx, displayInput ; display displayInput
mov edx, lenDisplayInput ; length of displayInput
int 0x80 ; call sys_write
mov eax, 4 ; specify sys_write call
mov ebx, 1 ; specify stdout file descriptor
mov ecx, number ; pass address of the number to write
mov edx, 5 ; pass number of numbers to write
int 0x80 ; call sys_write
Exit:
mov eax, 1 ; specific sys_exit call
mov ebx, 0 ; return code 0 to OS
int 0x80 ; call sys_exit
(Since you accepted this answer, I'll point out that the actual answer to this question about using read on TTYs is my other answer on this question.)
Here's an answer to your low-quality followup question which I was about to post when you deleted it.
Note that I said "you can ask for debugging help in a new question", not that you should ask 3 different questions in one, and re-post your whole code barely changed with no serious attempt at solving your own problem. It's still up to you to make the new question a good question.
I probably wouldn't have answered it if I hadn't sort of led to you posting it in the first place. Welcome to StackOverflow, I'm being generous since you're new and don't know what's a good question yet.
The usual term for the characters '0' through '9' is "digit", not "integer". It's much more specific.
ensure only integers are inputted in the buffer
You can't. You have to decide what you want to do if you detect such input.
Need help creating an array to loop through
Your buffer is an array of bytes.
You can loop over it with something like
# eax has the return value from the read system call, which you've checked is strictly greater than 0
mov esi, number ; start pointer
scan_buffer:
movzx edx, byte [esi]
# do something with the character in dl / edx
...
inc esi ; move to the next character
dec eax
jnz scan_buffer ; loop n times, where n = number of characters read by the system call.
ensure characters over the 1024 buffer do not send data to the tty
If you're worried that 1024 isn't necessarily big enough for this toy program, then use select(2) or poll(2) to check if there's more input to be read without blocking if there isn't.