Programming Forums - [MASM32] Working with arrays

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Klarre

Mar 3rd, 2008 2:34 PM

[MASM32] Working with arrays

Hi!

I am working on a system managing key presses in a MASM application. The problem is that I must be doing something wrong with the array that keeps the press status of each key. (bool g_keys[256] // Position 0x20 means VK_SPACE i e.)

The "input_set_key" function always returns a non-zero value like my memset hasn't done anything with the array.

What can be the problem? I can't see it...
Thanks alot for your helpfulness!

/Klarre



.data



g_keys dd 0        ; Pointer to the array of keys



.code



; ------------------------------------------------------------------------------

input_create proc

        invoke crt_malloc, 256        ; Allocate 256 Bytes for the key array

        mov g_keys, eax        ; Store the key array pointer



        invoke crt_memset, g_keys, 0, 256        ; Make sure no buttons are pressed



        invoke input_is_key_pressed, 27        ; DEBUG TEST. Returns a non-zero value



        xor eax, eax



        ret

input_create endp



; ------------------------------------------------------------------------------

input_is_key_pressed proc key:dword

        lea eax, [g_keys]        ; Get the key array address

        add eax, key        ; Offset to the correct position in the array

        mov eax, [eax]                ; Read the value on the position in the array



        ret

input_is_key_pressed endp



end

Klarre

Mar 3rd, 2008 3:21 PM

Re: [MASM32] Working with arrays

After finding the "Memory" debug window in Visual Studio, it was pretty simply to solve the bug. The functions is now looking like this and seems to work fine.

; ------------------------------------------------------------------------------

input_create proc

        invoke crt_malloc, 256        ; Allocate 256 Bytes for the key array

        mov g_keys, eax        ; Store the key array pointer



        invoke crt_memset, g_keys, 0, 256        ; Make sure no buttons are pressed



        ret

input_create endp



; ------------------------------------------------------------------------------

input_is_key_pressed proc key:dword

        mov eax, g_keys        ; Get the key array address

        add eax, key        ; Offset to the correct position in the array

        mov ah, [eax]        ; Read the value on the position in the array



        .if(ah)

                mov eax, 1

        .else

                mov eax, 0

        .endif



        ret

input_is_key_pressed endp

Irwin

Mar 9th, 2008 7:24 AM

Re: [MASM32] Working with arrays

IsKeyPressed proc Key:DWORD

    mov   ecx, [dwKey]

    movzx eax, byte [gKeys+ecx]

    test  eax, eax

    sete  al

    ret

IsKeyPressed endp



InputCreate  proc

    push  256d

    push  GPTR ; memory is filled with 0's

    call  GlobalAlloc

    push  27d

    push  IsKeyPressed

    ret

InputCreate endp

Also, a word to the wise. Don't use MSVCRT in ASM, it completely destroys the purpose of using ASM. The converting is fairly easy too:

malloc -> GlobalAlloc
memset -> stosb/stosw/stosd/stosq

Klarre

Mar 9th, 2008 1:55 PM

Re: [MASM32] Working with arrays

Thanks for your input Irwin. I removed the msvcrt dependency from my project and changed the malloc function call to HeapAlloc since I read on MSDN that GlobalAlloc wasn't recommended.

Another question you may be able to answear on: Is it possible to link a program using the Visual Studio linker without linking with msvcrt.lib? I have set the entry point to main, but still got two linker errors I can't get rid of. So I guess it is impossible, right?

Error        1        error LNK2001: unresolved external symbol __RTC_Shutdown        main.obj

Error        2        error LNK2001: unresolved external symbol __RTC_InitBase        main.obj

Irwin

Mar 10th, 2008 2:30 AM

Re: [MASM32] Working with arrays

Quote:

Originally Posted by Klarre (Post 142259)

Error        1        error LNK2001: unresolved external symbol __RTC_Shutdown        main.obj

Error        2        error LNK2001: unresolved external symbol __RTC_InitBase        main.obj

HeapAlloc is only recommended for small buffers, so for anything from 64-1024 bytes I use GlobalAlloc (then use VirtualAlloc for anything larger). Anyway, for a function like GetKeyboardState (which I assume you're using), I would use GlobalAlloc.

Also, you can completely remove any CRT dependency from an application by adding the /NODEFAULTLIB linker flag, then coupling it with the /entry:main (or whatever your entry function is called).

Klarre

Mar 10th, 2008 5:02 AM

Re: [MASM32] Working with arrays

Ah, I see. Going to read up a little bit about the alloc functions.

I am using the /NODEFAULTLIB linker flag and have set the entry point. But this will not get rid of the linker errors...

Irwin

Mar 10th, 2008 6:51 AM

Re: [MASM32] Working with arrays

Quote:

Originally Posted by Klarre (Post 142285)

Ah, I see. Going to read up a little bit about the alloc functions.

I am using the /NODEFAULTLIB linker flag and have set the entry point. But this will not get rid of the linker errors...

Post your complete source and assembler/link flags and I'll find your problem.

Klarre

Mar 10th, 2008 7:23 AM

Re: [MASM32] Working with arrays

The source file:

int main() { return 0; }

The linker command line (debug configuration):

/OUT:"G:\workspace\linktest\linktest\Debug\linktest.exe" /INCREMENTAL /NOLOGO /MANIFEST /MANIFESTFILE:"Debug\linktest.exe.intermediate.manifest" /NODEFAULTLIB /SUBSYSTEM:CONSOLE /ENTRY:"main" /MACHINE:X86 /ERRORREPORT:PROMPT

Causes these errors:

1>Linking...

1>main.obj : error LNK2001: unresolved external symbol __RTC_Shutdown

1>main.obj : error LNK2001: unresolved external symbol __RTC_InitBase

1>G:\workspace\linktest\linktest\Debug\linktest.exe : fatal error LNK1120: 2 unresolved externals

The linker command line (release configuration):

/OUT:"G:\workspace\linktest\linktest\Release\linktest.exe" /INCREMENTAL:NO /NOLOGO /MANIFEST /MANIFESTFILE:"Release\linktest.exe.intermediate.manifest" /NODEFAULTLIB /SUBSYSTEM:CONSOLE /OPT:REF /OPT:ICF /LTCG /ENTRY:"main" /MACHINE:X86 /ERRORREPORT:PROMPT

Causes these errors:

1>Linking...

1>main.obj : error LNK2001: unresolved external symbol @__security_check_cookie@4

1>G:\workspace\linktest\linktest\Release\linktest.exe : fatal error LNK1120: 1 unresolved externals

Klarre

Mar 10th, 2008 10:40 AM

Re: [MASM32] Working with arrays

Oh, I meant in a C++ project, which I forgot to mention in the earlier posts.

Irwin

Mar 10th, 2008 10:41 AM

Re: [MASM32] Working with arrays

Oh, the problems aren't in your linking flags but rather your compiler flags. Just add /GS- to your compiler flags.

Good luck :)

Also, it's fine; I also code in C(++) :P

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