Proper Way to write to shared memory Windows - c

Question

I have 2 processes, 1 process needs to write to a shared memory segment, the other process needs to read from the shared memory segment. The writing process only writes to shared mem, the reading process only reads.
Writing process
HANDLE hMapFile;
LPCTSTR pBuf;
char* Message = "test";
int MessageSize = 5;
hMapFile = CreateFileMappingA(INVALID_HANDLE_VALUE, NULL, PAGE_EXECUTE_READWRITE, 0, Size, SegmentName);
if (hMapFile == NULL)
{
printf("Could not create file mapping object (%d).\n", GetLastError());
return NULL;
}
pBuf = (LPTSTR)MapViewOfFile(hMapFile, FILE_MAP_ALL_ACCESS, 0, 0, Size);
if (pBuf == NULL)
{
printf("Could not map view of file (%d).\n", GetLastError());
//CloseHandle(hMapFile);
return NULL;
}
CopyMemory((PVOID)pBuf, Message, MessageSize);
Shortly after my reading process will read the message like so
HANDLE hMapFile;
LPCTSTR pBuf;
hMapFile = OpenFileMapping(FILE_MAP_ALL_ACCESS, FALSE, SegmentName);
if (hMapFile == NULL)
{
printf("Could not open file mapping object MINER PROC (%d).\n", GetLastError());
exit(0);
//return RetVal;
}
RetVal = (LPTSTR)MapViewOfFile(hMapFile, FILE_MAP_ALL_ACCESS, 0, 0, Size);
if (RetVal == NULL)
{
printf("Could not map view of file (%d).\n", GetLastError());
CloseHandle(hMapFile);
exit(0);
//return RetVal;
}
UnmapViewOfFile(hMapFile);
CloseHandle(hMapFile);
This works perfectly for a 1 time write then read. I need the writing process to be able to change the values.
I've tried this in the writing process
memset((PVOID)pBuf, '\0', strlen(OriginalMessage));
CopyMemory(pBuf, "newmessage",
strlen("newmessage") + 1);
But this gives me random crashes in the writing process, although the reading process seems to be able to read the changes fine.
I've also tried to close the segment like this from the writing process immediately after CopyMemory() call
UnmapViewOfFile(pBuf);
CloseHandle(hMapFile);
But then the memory disappears and the reading process cannot read the segment name. I also tried calling UnmapViewOfFile() & CloseHandle() then creating a new memory segment with the same name and I keep getting random crashes after that.
What is the proper way to change a shared memory value of a given shared memory segment name without crashes? Thanks.
EDIT - I'd like to add that I tested this code using the described methods (creating new shared memory segments) on 4 Win10 machine, 2 Win7 machines and I got no crashes. The crashes only occur on a Win8.1 machine. it's quite odd.
EDIT2 - also, all functions are successful in both the reading and writing processes when the crash occurs.