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void pointer

 
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void pointer, conversion
Jingle
post 7 Aug, 2008 - 01:30 PM
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How can You convert a void * to a const char *?
I tried this, but it didnt work..

CODE

void kill( void * vszProc )
{
const char * szProc = (const char *)vszProc;


It didnt give me an error, until i tried to use it. Then my application crashed.
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Tom9729
post 7 Aug, 2008 - 01:53 PM
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It's probably giving you a warning. If you're using GCC you can enable them with the -Wall compiler flag.
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Jingle
post 7 Aug, 2008 - 01:58 PM
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Visual Studio 6

It Doesnt Give me a warning either....

Im trying to use _beginthread() to create a new thread from this function, and give it the name of the process to kill.
But whenever i use the const char *, it gives me an empty string, and crashes.
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perfectly.insane
post 7 Aug, 2008 - 02:24 PM
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And what are you passing to the thread function via. _beginthread? (meaning, what does your _beginthread and any related string code look like)?

If you're casting the corresponding argument on the other side appropriately, then you might want to make sure that the string isn't stored on the function stack (or any function stack that might not be valid by the time your thread is run). Your string should either be a literal only, or it probably should have been created with malloc/new (or possibly a global statically allocated array/string).

This post has been edited by perfectly.insane: 7 Aug, 2008 - 02:28 PM
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Jingle
post 7 Aug, 2008 - 02:27 PM
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the thread starts fine... its just the void pointer conversion....

i am doing it like this:
CODE

_beginthread(kill, 0, "IXPLORE.EXE");


i even tried making a msgbox to display the const char *, to see if it would work:
CODE

MessageBox(NULL, szProc, "Test", MB_OK);


But this only gives me an empty messagebox
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perfectly.insane
post 7 Aug, 2008 - 02:47 PM
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In the thread, you could use something like this:

printf("vszProc = 0x%08x\n", vszProc);
printf("szProc = 0x%08x\n", szProc);

To see what the pointer addresses are. Just for diagnostic purposes. Doing this should not crash the program, as you're not dereferencing the pointers, just looking at the values. The values themselves will give you a clue as to where they're coming from. I'm guessing that the values should be approximately 0x004xxxxx or higher.

This post has been edited by perfectly.insane: 7 Aug, 2008 - 02:49 PM
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Jingle
post 7 Aug, 2008 - 02:54 PM
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I Could try that... but its a Windows dialog application, not a console one..
But it should just open a console if i printf if i remember right... i'll check it out
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perfectly.insane
post 7 Aug, 2008 - 03:01 PM
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No, it won't (unless you have some hacked printf that calls AllocConsole). You could do this instead.

char szMessage[80];
sprintf(szMessage, "vszProc = 0x%08x", vszProc);
MessageBoxA(NULL, szMessage, "Debug", MB_OK);
sprintf(szMessage, "szProc = 0x%08x", szProc);
MessageBoxA(NULL, szMessage, "Debug", MB_OK);

This post has been edited by perfectly.insane: 7 Aug, 2008 - 03:08 PM
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Jingle
post 7 Aug, 2008 - 03:08 PM
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Ok Ill Try That.
But What Do the Addresses Do For Me?
I Still want to get the Value from one into the other.
The Only Thing that i can see coming from this is that they both have an address...
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perfectly.insane
post 7 Aug, 2008 - 03:12 PM
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If the correct pointer value is transferred, then you should be able to read the string at that address. Looking at the pointer value, you should be able to make sure that your pointer value is at least in a realistic range (such as 0x004xxxxx, not 0x99999999, 0x00000000, etc.)

NOTE: you cannot WRITE to that memory area, because it's read only (all string literals are).
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Jingle
post 7 Aug, 2008 - 03:16 PM
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Ok ill check it out...
but im a little busy right now..
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