How much memory can CreateFileMapping request? - c++

Question

I want to use shared memory to transfer large images (10M or more) between two processes, but I can only request 4096 bytes of BUF_SIZE when requesting shared memory.beyond 4096 bytes, the program will crash.
Here is my code:
hMapFile = CreateFileMappingW(
INVALID_HANDLE_VALUE, // use paging file
NULL, // default security
PAGE_READWRITE, // read/write access
0, // maximum object size (high-order DWORD)
BUF_SIZE, // maximum object size (low-order DWORD)超过4096就不行了，不知道怎么解决
szMapName);
My system is windos64, Use C++ in qt.anyone have the same problem as me?
I think I know why the program crashed. It's because there's something wrong with the code below.
hMapFile = CreateFileMappingW(
INVALID_HANDLE_VALUE, // use paging file
NULL, // default security
PAGE_READWRITE, // read/write access
0, // maximum object size (high-order DWORD)
BUF_SIZE, // maximum object size (low-order DWORD)
szMapName); // name of mapping object
if (hMapFile == NULL){
qDebug() << (TEXT("Could not create file mapping object (%d).\n"),GetLastError());
return -1;
}
pBuf = (LPTSTR)MapViewOfFile(
hMapFile, // handle to map object
FILE_MAP_ALL_ACCESS, // read/write permission
0,
0,
4097);//if this number > 4096, the program will stuck
if (pBuf == NULL){
qDebug() << (TEXT("Could not map view of file (%d).\n"),
GetLastError());
CloseHandle(hMapFile);
return -1;
}

Answer 1

You called CreateFileMappingW with BUF_SIZE as the low order DWORD size (with the high order DWORD being 0, so BUF_SIZE is the total number of bytes). That's the limit on what you can map later with MapViewOfFile. I'm guessing you defined BUF_SIZE as a constant 4096 somewhere, so that's the limit on what MapViewOfFile can map. Use a larger number for CreateFileMappingW and MapViewOfFile can increase to match.