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Assigning value to a pointer to a typedef'ed variable

Cheat Engine Forum Index -> General programming

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Anden100
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Posted: Wed Jul 29, 2009 10:20 am Post subject: Assigning value to a pointer to a typedef'ed variable

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I've created a source, that looks something like this:

Code:

typedef BOOL (WINAPI CrtProc)(__in_opt LPCSTR lpApplicationName, __inout_opt LPSTR lpCommandLine, __in_opt LPSECURITY_ATTRIBUTES lpProcessAttributes, __in_opt LPSECURITY_ATTRIBUTES lpThreadAttributes, __in BOOL bInheritHandles, __in DWORD dwCreationFlags, __in_opt LPVOID lpEnvironment, __in_opt LPCSTR lpCurrentDirectory, __in LPSTARTUPINFOA lpStartupInfo, __out LPPROCESS_INFORMATION lpProcessInformation);
CrtProc* crtProc;
...
DWORD codeaddr = 0xDEADBEEF; //of curse not, but its a block of allocated memory
...
crtProc = (CrtProc (__stdcall *))codeaddr;

ass you clearly see, i apply the DWORD to crtProc using this line:

Code:

crtProc = (CrtProc (__stdcall *))codeaddr;

But i was wondering if there is any other way to put the value of codeaddr into crtProc, so that i can be other typedefs, and not just CrtProc?, i've been attempting with (void*), etc, etc, but i didnt manage to get it to work properly...

Any advice would be nice here...

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Noz3001
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Posted: Wed Jul 29, 2009 3:03 pm Post subject:

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Something like this?

Code:

CrtProc* crtProc = (CrtProc*)0x12345;

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Anden100
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Posted: Wed Jul 29, 2009 3:19 pm Post subject:

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Noz3001 wrote:

Something like this?

Code:

CrtProc* crtProc = (CrtProc*)0x12345;

I want to pass crtProc as a void* to a function, like this:

Code:

void function(DWORD value, void* crtProc){
crtProc = value; //How would i do this?
}

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Dark Byte
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Posted: Wed Jul 29, 2009 4:28 pm Post subject:

Problem with a void type is that it's nothing, so has to be typecast to the type you want to use it as first. I assume you want to write a DWORD value there, so typecast it to a DWORD pointer first, then dereference the pointer and write to it: (DWORD )crtProc=value; _________________ Tools give you results. Knowledge gives you control. Like my help? Join me on Patreon so i can keep helping

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Anden100
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Posted: Thu Jul 30, 2009 1:57 am Post subject:

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Dark Byte wrote:

Problem with a void type is that it's nothing, so has to be typecast to the type you want to use it as first.
I assume you want to write a DWORD value there, so typecast it to a DWORD pointer first, then dereference the pointer and write to it:
*(DWORD *)crtProc=value;

I did attempt to do that, but since the pointer isn't in any way assigned, it gives me:

Code:

Unhandled exception at 0x00281153 in CreateProcessHook.exe: 0xC0000005: Access violation writing location 0x00000000.

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smartz993
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Posted: Thu Jul 30, 2009 2:49 am Post subject:

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Here nig.

Code:

typedef void (WINAPI CrtProc)(char* cBuffer);
CrtProc* crtProc = (CrtProc*)0xDEADBEEF;

void newFunc(char* cBuffer)
{
MessageBox(0,cBuffer,"funcptr changed!",0);
}

void oldFunc(char* cBuffer)
{
MessageBox(0,cBuffer,"funcptr change FAILED!",0);
}

void function(DWORD value, DWORD** crttProc)
{
*(DWORD*)crttProc = value;
}

.....

crtProc = (CrtProc*)oldFunc;
function((DWORD)&newFunc,(DWORD**)&crtProc);
crtProc("bawwwwwwwwwwwwwwwwww");

Works for me.

If it doesn't work, it will have "funcptr change FAILED!" in the title of the messagebox, or else it will say "funcptr changed!".

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