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assemblymasmmessageboxmasm32

messagebox not showing up in windows 10 masm

I'm trying to get into asm using masm32 but the simple sample code from the tutorial doesn't work

.386
.model flat,stdcall
option casemap:none

include \masm32\include\windows.inc
include \masm32\include\user32.inc

includelib \masm32\lib\user32.lib

.data
BUFFER_LENGTH EQU 1024
szMessageBoxFormat BYTE "The resul is %d", 0
szMessageBoxText BYTE 0 dup(BUFFER_LENGTH)

.code

start:

main proc
  push 3
  call display_number_in_message_box
  ret
main endp

display_number_in_message_box proc
  ;Create a string representation of the number
  mov eax, [esp + 4]
  invoke wsprintf, ADDR szMessageBoxText, szMessageBoxFormat, eax

  ;Display that string in a message box
  invoke MessageBoxA, NULL, ADDR szMessageBoxText, NULL, MB_OK

  ret 4
display_number_in_message_box endp

end start

I am using C:\masm32\bin\ml.exe /c /coff /Cp ex0.asm and C:\masm32\bin\link.exe /SUBSYSTEM:WINDOWS /LIBPATH:C:\masm32\lib ex0.obj to create an exe, but when running it nothing happens, any ideas?

Solution

  • You forgot the ADDR before szMessageBoxFormat when you invoke wsprintf, so you end up passing an invalid address (probably 20656854h, i.e. "The " interpreted as a DWORD).