Printable View
I created a mapped file, and mapview of a file as follows
hMap=CreateFileMapping(hFile, 0, PAGE_READWRITE, 0,0,0);
lpBaseAddr=(LPBYTE)MapViewOfFile(hMap,FILE_MAP_WRITE,0,0,0);
pImgHdr=Checksummapfile(lpBaseAddr,nFileSize,&dwOldSum,&dwNewSum);
The third line in debuging produces error of Access Violation.
Could someone who knows about this offers me some guidance please ? :(
Thank you.
Either something fail so lpBaseAddr is NULL or you do something bad in Checksummapfile. Single-step your code in the debugger and check the result from every single line.
Access violation will typically mean that you are trying to access a relative offset in the filemapping that exceeds the mapped file.
As in you have a file of 10 bytes, and you are trying to read/write the byte at lpBaseAddr+10
Access violation is pointer error. The code snippet you posted doesn't make any check on nFileSize, hFile, hMap, lpBaseAddress though any of these handles, sizes, pointers could be invalid. I would bet that either lpBaseAddress is NULL or nFileSize is invalid and that the crash is because of that.
Thank you everyone for your ideas, I changed pointers into references and the problem went away. :)
However, I am still stuck on the NULL return of the function, the dwOldSum always becomes zero. MSDN doesn't provide information why that is so. GetLastError after the CheckSumMappedFile also offers a value of 0 which states nothing about the extended error itself. :( Somebody helps me please?
I did this in VS2005 and it worked alright as far as I understand itSince all functions return success I can only presume that the original checksum is 0. In http://msdn.microsoft.com/en-us/libr...(v=VS.85).aspx it's statedCode:DWORD hdrsum, chksum;
DWORD retval = MapFileAndCheckSum( "../debug/console.exe", &hdrsum, &chksum );
// retval = 0, hdrsum = 0, chksum = 0xdf68
HANDLE hFile = CreateFile( "../debug/console.exe", GENERIC_READ, 0, 0, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, 0 );
DWORD size = GetFileSize( hFile, 0 ); // Don't need high-order DWORD
HANDLE hMap = CreateFileMapping( hFile, 0, PAGE_READONLY, 0, 0, 0 );
LPVOID lpBaseAddr = MapViewOfFile( hMap, FILE_MAP_COPY, 0, 0, 0 );
IMAGE_NT_HEADERS* pHdrs = CheckSumMappedFile( lpBaseAddr, size, &hdrsum, &chksum );
// pHdrs = 0x3c00e8, hdrsum = 0, chksum = 0xdf68
UnmapViewOfFile( lpBaseAddr ); // Unchecked return...
CloseHandle( hMap );
CloseHandle( hFile );
and, yes they were right... in my project the Set Checksum option was No so I changed it to Yes and voila! :)Quote:
The linker computes the original checksum at link time, if you use the appropriate linker switch. For more details, see your linker documentation.