macro PrintString [args]
{ 
    local ..startm , ..endm
    jmp ..endm
    ..startm:
    common db args,0
    ..endm:
    mov rax, ..startm
    mov rcx, ..endm - ..startm
}
    

C:\fasm>fasm invoke-messagebox.fasm
flat assembler version 1.73.32 (1048576 kilobytes memory)
invoke-messagebox.fasm [451]:
PrintString "Big whoppers","of things!"
invoke-messagebox.fasm [146] PrintString [5]:
..endm:
processed: ..endm?T0,..endm?T2:
error: illegal instruction.

  PrintString "Big whoppers","of things!"  ; strings to be joined together
  invoke MessageBox, 0, rax, "Joined", MB_OK
    

invoke MessageBox, HWND_DESKTOP, <"First string", "Second string", "Third string">, "Test", MB_OK or MB_ICONINFORMATION    

EOLN fix 0xd,0xa

struc StringA txt& { label .
  db txt
  label .length at ( $ - . )
  db 0
  label .bytes at ( $ - . ) }
; ...
        invoke WriteFile, [hFile], addr [a], a.length, addr [nWriten], NULL
; ...
a StringA "First string", EOLN, "Second string", EOLN, "Third string"
    

My newbie brain hurts and wonders...

"Joined: 15 Jul 2004"

<examples>

jmp @@
@1: db 'Here lies a very deep, introspective string,'\
       "which may even continue on multiple lines.',13,10,0
@2: db $ - @1
@@:
  mov rcx, [@2]
  mov rdx, @1
[...call/invoke something...]
    

  jmp  @f
@1: db 'Here lies a very deep, introspective string,',\
       "which may even continue on multiple lines.",13,10,0
@2: dq $ - @1
@@:
  mov  rcx, [@2]
  lea  rdx, [@1]
[...call/invoke something...]    

I notice Thomas made some macros which might fit the purpose at
https://board.flatassembler.net/topic.php?p=190642#190642
but for Fasmg only. Any chance those could be translated to plain Fasm?

macro @INIT name,prefix
{
        macro name tail&
        \{
                match label, prefix#f
                \\{
                        label tail
                        prefix#b equ prefix#f
                        prefix#r equ prefix#f
                \\}
                \local ..anonymous
                prefix#f equ ..anonymous
        \}

        define prefix#f
        name
}

rept 10 i:0
{
        @INIT @#i,@#i
}    

'Here lies a very deep, introspective string,'\
"which may even continue on multiple lines.',13,10,0

macro PrintString [args]
{
    common
      local startm, endm, count
      count = 0
      jmp endm
      startm:
    forward
      count=count+1
    forward
      db args
      if ~ count = 1
        count=count-1
        db 0xd,0xa
      end if
    common
      db 0
      endm:
      mov rax, startm            ; string address
      mov rcx, endm - startm - 1 ; string size (minus 1 null)
}

PrintString "Here lies a very deep, introspective string",\
            "which may even continue on multiple lines."    

if last
 db 0
end if
if not last
 db 0xA
end if    

if current_param = -1
 db 0
end if    

If the string is a counted length then you don't need the 0 terminator.

Or alternatively, if the string is zero terminated then you don't need the length.

A way to conveniently use throwaway strings within code without endless label inventing, or even keeping track of a serial#.

If the string is a counted length then you don't need the 0 terminator.

Or alternatively, if the string is zero terminated then you don't need the length.

if only fasm would had a convenient way to detect the last parameter, u know by something like this: ...

macro PrintString args&
    local startm, endm
    jmp endm
    startm:
    iterate item, args
        db item
        if % < %%
          db 0xd,0xa
        end if
    end iterate
    db 0
    endm:
    mov rax, startm
    mov rcx, endm - startm - 1
end macro    

revolution wrote:

If the string is a counted length then you don't need the 0 terminator.

Or alternatively, if the string is zero terminated then you don't need the length.

Controversial statements, at least because then the strings will not be interchangeable and you will have to spend time calculating the length.

; Better for WriteConsole/File, easy usage
@@: msg_debug     dq @f - @b - 8  ; current data size (dq) needs to be subbed
    db 'Attempting to write a console message...', 13, 10, 0
    ; String always at msg_debug + datatype_size; pick one type and stick with it
;
; Note the next anon label is still part of the definition
;
; Better for printf but need to specify size with length operations
@@: dq @f - @b - 8
    ; Address always at string_label - datatype_size
    msg_debug_3 db 'Attempting to write a console message yet again...', 13, 10, 0
@@: ; If using label after length version, size must be specified when using length:
    ; mov r8, qword [msg_debug_3 - 8]
    

You can translate the macros made for fasmg quite directly

Please do prove me wrong..).

(as testified by the lack of solutions this far, or did my searches fail? Please do prove me wrong..).

macro @@@ colon { }

;fasm do this ?
if a eq colon or eqtype
 do some
end if
    

macro @@@ arg { }    

There is one from 2006, even.

include '@@.inc'