Printing an entire array on a single line using printf asm nasm

Question

I am using NASM for compiling my ASM program and I am having trouble figuring out how to print an entire array on a single line (without necessarily knowing how big the array is) using a loop. Whenever I create a loop with printf it prints the values on multiple lines instead of one line. Any idea how to make printf print multiple values of an array on a single line using a loop? I get values 1-9 but all on a different line instead of the same line. This is to be done without using external libraries other than: the printf c library. Any help would be most appreciated. The code I have is below.

  extern    printf  

 SECTION .data              ; Data section, initialized variables

array: dd 1, 2, 3, 4, 5, 6, 7, 8, 9, 0; this is a test array for testing purposes

arrayLen: dd 9  ; length of array 

aoutput: db "%d", 10, 0 ; output format

SECTION .text               ; Code section.

global main             ; the standard gcc entry point

main:                   ; the program label for the entry point
    push    ebp         ; set up stack frame
    mov     ebp,esp

    mov ecx, [arrayLen] ; loop counter set up
    mov esi, 0      ; counter to increment set up for looping through array
.loop:

    push ecx                                    ; make sure to put ecx (counter) on stack so we don't lose it when calling printf)
    push dword [array + esi]                    ; put the value of the array at this (esi) index on the stack to be used by printf
    push dword aoutput                          ; put the array output format on the stack for printf to use
    call printf                                 ; call the printf command
    add esp, 8                                  ; add 4 bytes * 2
    pop ecx                                     ; get ecx back

    add esi, 4
    loop .loop

    mov     esp, ebp    ; takedown stack frame
    pop     ebp         ; same as "leave" op

    mov     eax,0       ; normal, no error, return value
    ret                 ; return

@JonathonReinhart I agree with you. Ikegami thanks for trying to help, although when I am asking for some syntax for assembler, that is what I am seeking, because in another language like c++ i know how to make a new line or not make a new line when using something like cout, but with assembler the syntax is a little different, which is what I was asking about, because I already know what I am looking for (not adding the \n) but I was asking how not to add the \n, because I didn't know where that was put, anyways I found the answer I was seeking. Thanks all for helping. — , Feb 11 '15 at 19:28
Related: you might want to fflush if you don't print a newline at all: [Printf without newline in assembly](https://stackoverflow.com/q/8502945) — Peter Cordes, Feb 02 '21 at 21:00

score 2 · Accepted Answer · answered Feb 11 '15 at 19:13

The only thing that determines whether something is printed on a single line or multiple, is if you print a newline character (\n) or not.

Here, when you say 10, that is the ASCII value for a Line Feed. If you change this:

aoutput: db "%d", 10, 0

to this:

aoutput: db "%d ", 0

your values will be separated by spaces, instead of by new lines.

After the final value in the sequence, you can print a lone newline character:

push 0x0A     ; New line character
call putchar

Note that your solution leaves an trailing space. This can be annoying and can cause blank lines on the screen. — ikegami, Feb 11 '15 at 21:21

score 0 · Answer 2 · answered Feb 11 '15 at 19:21

0

I figured out this (which is the same as the other answer, I just found it out before I saw it was posted).

I figured it out, I changed the format definition to:

 aoutput: db "%d ", 0   ; output format

from:

 aoutput: db "%d ", 10, 0   ; output format

and just added an newline format to add a new line at the end.

 newline: db "", 10, 0    ; newline format

answered Feb 11 '15 at 19:21

FWIW, Nasm will recognise "\n" and the other escape sequences if you enclose your string in "back quotes" (the character we use here to indicate code) - not single or double quotes. – Frank Kotler Feb 11 '15 at 21:59

ikegami · Answer 3 · 2015-02-11T22:20:06.447

The problem is that you are outputting a line feeds after each element.

What follows are two solution. Neither of them suffer from the problem of leaving a trailing blank space as the two existing solutions do.

Note that I made a slight rearrangement of the loop to allow empty arrays. Allowing empty arrays is a good practice even if it's not necessary since it doesn't require any extra instructions.

Solution 1: Use "%d\n" as the format if it's the last element or "%d " otherwise.

This is good if you don't want to print the line feed for empty arrays.

format1: db "%d ", 0
format2: db "%d", 10, 0

    jmp .loop3

.loop1:
    mov eax,format1
    cmp ecx,1
    jnz .loop2

    mov eax,format2

.loop2
    push ecx
    push dword [array + esi]
    push dword eax
    call printf
    add esp, 8
    pop ecx

    add esi, 4

.loop3:
    loop .loop1

Solution 2: Use "%d" as the format if it's the first element. Use " %d" as the format otherwise. Print a line feed after the loop.

This is good if you want to print the line feed even for empty arrays.

format1: db "%d", 0
format2: db " %d", 0

    mov eax, format1
    jmp .loop2

.loop1:
    push ecx
    push dword [array + esi]
    push dword eax
    call printf
    add esp, 8
    pop ecx

    add esi, 4
    mov eax, format2

.loop2:
    loop .loop1

    push 10
    call putchar

Pardon any errors; the x86 didn't have an eax register the last time I wrote assembly for it. The logic should be evident in any case.

Printing an entire array on a single line using printf asm nasm

3 Answers3

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