Console I/O from windows application

[WillofIrony]

Is it possible for a windows application to output to a console window via stdout? This would be only for debugging. If so, how would this be implimented?

Thanks in anticipation

[Mark Jones]

Hi Michael. It is possible to specify console window creation in the linker via "/SUBSYSTEM:CONSOLE" even in graphical applications, which will generate the console window in addition to the main window. My DWG application found here does something like this. I am unsure of any limitations or ramifications of doing this, but perhaps this may be useful. Also as a shortcut, "print xxx" can work in place of StdOut in writing to the console window where XXX is an ascii string address "print myString" or a combined macro such as 'print chr$("Hello world!",13,10)'

[evlncrn8]

or if your program is gui (and has to be) then you can do AllocConsole
and use GetStdHandle to obtain the handles needed for output/input

[jj2007]

Hi Michael. It is possible to specify console window creation in the linker via "/SUBSYSTEM:CONSOLE"  ... or a combined macro such as 'print chr$("Hello world!",13,10)'

For debugging, str$() is a very useful macro. Here is an example:

Code Select Expand


include \masm32\include\masm32rt.inc

.code

MsgText db "This is a tiny console application",13,10,0

start:
print Offset MsgText
print chr$("Eax contains ")
mov eax,123456789
print str$(eax)
invoke ExitProcess,eax
end start


It works, but watch your step: after "print", eax is no longer what it was before.

And here is the console.bat batch file used, assuming you use *.asc as extension for a console app:

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REM to be placed in \MASM32 !!
@echo off

echo Assembling and running %1.asc

if exist %1.obj del %1.obj
if exist %1.exe del %1.exe

\MASM32\BIN\ML.EXE /c /coff %1.asc
if errorlevel 1 goto errasm

echo assembled OK, now linking

\MASM32\BIN\LINK.EXE /SUBSYSTEM:CONSOLE %1.obj

if errorlevel 0 goto Perfect

echo.
echo Link error
pause
goto TheEnd

:errasm
echo Assembly Error
pause
goto TheEnd

:Perfect
echo assembled and linked OK

echo -------------------------------------------- CONSOLE OUTPUT -----------------
echo.
%1.exe
if exist %1.obj del %1.obj
echo.
echo -------------------------------------------- CONSOLE OUTPUT -----------------
:TheEnd
pause
CLS


[Vortex]

Stdout is using internally the eax register, this is why eax is not preserved :

print MACRO arg1:REQ,varname:VARARG      ;; display zero terminated string
        invoke StdOut,reparg(arg1)
      IFNB <varname>
        invoke StdOut,chr$(varname)
      ENDIF
    ENDM

Here is a modified version of the code above :

Code Select Expand

.386
.model flat,stdcall
option casemap:none

include consoleIO.inc

.data
message db 'Console I/O from windows application',0
capt    db 'Hello',0
MsgText db 13,10,'This is a tiny console application',13,10
        db 'Hit RETURN to terminate the application',13,10,0

.data?
buffer  db 10 dup(?)

.code

start:

    invoke  MessageBox,0,ADDR message,ADDR capt,MB_OK
    invoke  AllocConsole
    print   chr$("eax contains ")
    mov     eax,123456789
    print   str$(eax)
    print   OFFSET MsgText
    invoke  StdIn,ADDR buffer,10
    invoke  FreeConsole
    invoke  ExitProcess,eax

END start
[attachment deleted by admin]

[P1]

Then there is the traditional windows debug using something like DebugView to watch output.

Some conditional coding to build a debug build of your app.

Code Select Expand

g_Debug equ TRUE

ifdef g_Debug
    invoke OutputDebugString, addr szDLL_PROCESS_ATTACH
endif   


Regards,  P1   :8)

[Vortex]

Also, not to forget Vkim's debugging tool coming with the Masm32 package :

Code Select Expand

\masm32\vkdebug

VKDEBUG is a debugging tool for the MASM32 package. For more information
see dbgwin.hlp

[redskull]

also, just for completness, there's a std_err output handle as well as std_in and std_out; that way you can keep your regular output going wherever it needs to go, and just dump out errors to the screen or something equally as neat.

[jj2007]

Stdout is using internally the eax register, this is why eax is not preserved :

print MACRO arg1:REQ,varname:VARARG      ;; display zero terminated string
        invoke StdOut,reparg(arg1)
      IFNB <varname>
        invoke StdOut,chr$(varname)
      ENDIF
    ENDM

I am afraid print/StdOut also uses ecx and edx, see my GetLogicalDrive code at http://www.masm32.com/board/index.php?topic=8118.msg59349#msg59349 and the test code below:

--- Output: ---
Testing all registers:
eax 6
ebx 1234567891
ecx 2088832534
edx 2089872276
esi 1234567894
edi 1234567895

Code Select Expand


include \masm32\include\masm32rt.inc

.code

start: pushad ; save all regs
print chr$("Testing all registers:")
mov eax,1234567890
inc eax
mov ebx,eax ;891
inc eax
mov ecx,eax ;892
inc eax
mov edx,eax ;893
inc eax
mov esi,eax ;894
inc eax
mov edi,eax ;895
mov eax,1234567890

print chr$(13,10,"eax ")
print str$(eax)
print chr$(13,10,"ebx ")
print str$(ebx)
print chr$(13,10,"ecx ")
print str$(ecx)
print chr$(13,10,"edx ")
print str$(edx)
print chr$(13,10,"esi ")
print str$(esi)
print chr$(13,10,"edi ")
print str$(edi)

popad
invoke ExitProcess,eax
end start


[hutch--]

jj,

> I am afraid print/StdOut also uses ecx and edx,

This is normal in a procedure, EAX, ECX and EDX are volatile registers where the rest MUST be preserved in a procedure.