The problem isn't that BytesWritten is not a pointer, it
is that you don't have it pointing to any valid location
which is why the crash in WriteFile().
--Chris
On 1/10/2016 07:31, Ben Hutchinson
wrote:
When I try to compile this:
#include <windows.h>
int _start(void){
unsigned char MyArray[4];
LPDWORD BytesWritten;
HANDLE hFile;
hFile=CreateFile("MyFile.dat",0xC0000000,0,0,2,0,0);
MyArray[0]=1;
MyArray[1]=2;
MyArray[2]=3;
MyArray[3]=4;
WriteFile(hFile,MyArray,4,BytesWritten,0);
CloseHandle(hFile);
}
I get a program that crashes when I run it. When I look
at the dissassembly in OllyDbg, it turns out that what's
happening is that in the WriteFile line of code, it's
passing the value stored in BytesWritten, rather than its
memory address, even though BytesWritten has been declared
with LPDWORD, and even though LPDWORD has by defined (via
typedef) as a pointer. When a pointer type variable is
passed it should be passing the memory address, not the
value stored there, but passing the value stored there is
EXACTLY what's happening. The ONLY time that the value
stored at a pointer should be passed is when you prefface
that pointer with an asterisk. If I have a variable
declared like this:
LPDWORD MyPtr
Every time I use that pointer, including passing it
as a parameter in a function as just MyPtr, it SHOULD be
passing the memory address, not the value stored there.
The ONLY time that it should it should be using the value
stored in a pointer-type variable there is if I am using
an astrisk with it, like this:
*MyPtr
As you can see from the above code sample, my pointer-type
variable is being passed in such a way that it should be
passing the ADDRESS to the function, NOT passing the value,
yet passing the value is exactly what's happening, as I can
tell by running the program in a debugger.
This is a MAJOR glitch. It's what I call a "show stopper"
glitch. It is significant enough that it will prevent you from
from writing any decent program in TCC. I only wish the author
of this software didn't stop updating it back in 2013. There's
still quite a few bugs that are still NOT FIXED.
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