Memory map streaming data in C++ - c++

Question

I am collecting data from LiDAR in real time. I created a for loop to iterate over initiating a frame, collecting the data and saving it into an array (distArray). However, I am stuck with the memory mapping part. My array takes 500 integers ==> 2000 bytes of memory .. When I try to map each array element to memory using CopyMemory(), I am getting the following error "Exception thrown at 0x5843335E (vcruntime140d.dll) in file.exe: 0xC0000005: Access violation writing location 0x007E0000." .. Any ideas on how to solve this problem?
In the code below, there are a lot of functions and header calls that are irrelevant to the question, so please don't mind them ..
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <bta.h>
#include <windows.h>
#include <stdio.h>
#include <conio.h>
#include <tchar.h>
#define BUF_SIZE 2000
TCHAR szName[] = TEXT("mapObjFile");
void setTOFParameters(BTA_Handle btaHandle, uint32_t newTint, uint32_t newFPS, uint32_t newFMOD);
static void errorHandling(BTA_Status status);
const int arraySize = 500;
const int numFrames = 500;
int distArray[arraySize];
int main() {
BTA_Status status;
BTA_Config config;
printf("BTAinitConfig()\n\n");
status = BTAinitConfig(&config);
errorHandling(status);
uint8_t udpDataIpAddr[] = { 224, 0, 0, 1 };
config.udpDataIpAddr = udpDataIpAddr;
config.udpDataIpAddrLen = 4;
config.udpDataPort = 10002;
uint8_t tcpDeviceIpAddr[] = { 192, 168, 0, 10 };
config.tcpDeviceIpAddr = tcpDeviceIpAddr;
config.tcpDeviceIpAddrLen = 4;
config.tcpControlPort = 10001;
config.frameQueueMode = BTA_QueueModeDropOldest;
config.frameQueueLength = 500;
config.frameMode = BTA_FrameModeDistAmp;
// OPEN Connection
BTA_Handle btaHandle;
printf("BTAopen()\n\n");
status = BTAopen(&config, &btaHandle);
errorHandling(status);
printf("Service running: %d\n", BTAisRunning(btaHandle));
printf("Connection up: %d\n\n", BTAisConnected(btaHandle));
BTA_DeviceInfo *deviceInfo;
printf("BTAgetDeviceInfo()\n");
status = BTAgetDeviceInfo(btaHandle, &deviceInfo);
errorHandling(status);
printf("Device type: 0x%x\n", deviceInfo->deviceType);
printf("BTAfreeDeviceInfo()\n\n");
BTAfreeDeviceInfo(deviceInfo);
// READ Register
uint32_t regAddr = 0x1004; //MLX75123, Register 0x1000 = I2C_ADDRESS
uint32_t regValue;
status = BTAreadRegister(btaHandle, regAddr, &regValue, 0);
errorHandling(status);
printf("BTAreadRegister : Register 0x%04X has value 0x%04X\n\n", regAddr, regValue);
for (int i = 1; i < numFrames; i++) {
// GET The Frame
printf("Getting distance and amplitude data :\n");
BTA_Frame *frame;
printf("BTAgetFrame()\n");
status = BTAgetFrame(btaHandle, &frame, 300);
errorHandling(status);
BTA_DataFormat dataFormat;
BTA_Unit unit;
uint16_t xRes, yRes;
// Getting the distance data into a buffer and calculating the average amplitude over the entire frame :
uint16_t *distances;
printf("BTAgetDistances()\n");
status = BTAgetDistances(frame, (void**)&distances, &dataFormat, &unit, &xRes, &yRes);
errorHandling(status);
if (dataFormat == BTA_DataFormatUInt16) {
uint32_t distAvg = 0;
for (int y = 0; y < yRes; y++) {
for (int x = 0; x < xRes; x++) {
distAvg += distances[x + y * xRes];
}
}
if (xRes != 0 && yRes != 0) {
distArray[i] = distAvg / xRes / yRes;
printf("The average distance is %d.\n", distArray[i]);
}
}
// FREE The Frame
printf("BTAfreeFrame()\n\n");
status = BTAfreeFrame(&frame);
errorHandling(status);
// ----------------------- Memory Mapping -----------------------
HANDLE hMapFile;
LPCTSTR pBuf;
hMapFile = CreateFileMapping(
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)
szName); // name of mapping object
if (hMapFile == NULL)
{
_tprintf(TEXT("Could not create file mapping object (%d).\n"),
GetLastError());
return 1;
}
pBuf = (LPTSTR)MapViewOfFile(hMapFile, // handle to map object
FILE_MAP_READ, // read/write permission
0,
0,
BUF_SIZE);
if (pBuf == NULL)
{
_tprintf(TEXT("Could not map view of file (%d).\n"),
GetLastError());
CloseHandle(hMapFile);
return 1;
}
CopyMemory((PVOID)pBuf, &distArray, BUF_SIZE);
_getch();
/*UnmapViewOfFile(pBuf);
CloseHandle(hMapFile);*/
}
// CLOSE Connection
printf("BTAclose()\n\n");
status = BTAclose(&btaHandle);
errorHandling(status);
// END Program
printf("Hit <ENTER> to close the window .. ");
fgetc(stdin);
}
After mapping the data to the memory, I will be using the mmap library in Python (https://docs.python.org/3.0/library/mmap.html) to access the data based on the tagname parameter ...

Answer 1

See here: https://learn.microsoft.com/en-us/previous-versions/windows/desktop/legacy/aa366535(v%3Dvs.85)
void CopyMemory(
_In_ PVOID Destination,
_In_ const VOID *Source,
_In_ SIZE_T Length
);
first parameter is the destination, the second is source. But in your code you have:
CopyMemory((PVOID)pBuf, &distArray, BUF_SIZE);
... the other way around. So the exception is because you copy data from distArray to pBuf which is the mapping of read only memory.