Access violation reading location 0xc3618000 - c++

Question

I am working on a project about IR Tracking and I am using FreeTrack (www.free-track.net) software for it. FreeTrack offers a sdk folder with their download with C, Matlab and delphi code which can be used to interface the data from FreeTrack to your own writing program in one of these languages.
I started off with Matlab, but when matlab gave a problem, I went on to C++ in Mvisual. This also gives a problem, which seems like the same in Matlab.
Here is the thing:
When i want to read data from a DLL of the freetrack client, I use:
//declare imported function pointers
importGetData getData;
getData = (importGetData)GetProcAddress(hinstLib, "FTGetData");
if (getData(pData))
printf("Yaw: %f\n", data.yaw);
First time it works, but the data is 0. Second time it does it, Mvisual gives the error:
Unhandled exception at 0xc3618000 in FreeTrack.exe: 0xC0000005: Access violation
reading location 0xc3618000.
getData has the adres 0xc3618000.
This only happens when FreeTrack is running. When it isnt, No data is returned from getData.
Any idea's what this can be?
Original code:
#include <windows.h>
#include <stdio.h>
#include <conio.h>
typedef struct
{
float yaw;
float pitch;
float roll;
float x;
float y;
float z;
int dataID;
}FreeTrackData;
// DLL function signatures
// These match those given in FTTypes.pas
// WINAPI is macro for __stdcall defined somewhere in the depths of windows.h
typedef bool (WINAPI *importGetData)(FreeTrackData * data);
typedef char *(WINAPI *importGetDllVersion)(void);
typedef void (WINAPI *importReportID)(int name);
typedef char *(WINAPI *importProvider)(void);
int main(int argc, char **argv)
{
/*while(1){
printf("hello");
}*/
//declare imported function pointers
importGetData getData;
importGetDllVersion getDllVersion;
importReportID reportID;
importProvider provider;
// create variables for exchanging data with the dll
FreeTrackData data;
FreeTrackData *pData;
pData = &data;
char *pDllVersion;
int name = 453;
char *pProvider;
//while(1){};
// Load DLL file
HINSTANCE hinstLib = LoadLibrary("FreeTrackClient.dll");
if (hinstLib == NULL) {
printf("ERROR: unable to load DLL\n");
//return 1;
while(1){};
}
else
{
printf("dll loaded\n");
}
//while(1){};
// Get function pointers
getData = (importGetData)GetProcAddress(hinstLib, "FTGetData");
getDllVersion = (importGetDllVersion)GetProcAddress(hinstLib, "FTGetDllVersion");
//reportID = (importReportID)GetProcAddress(hinstLib, "FTReportID");
reportID = (importReportID)GetProcAddress(hinstLib, "FTReportName");
provider = (importProvider)GetProcAddress(hinstLib, "FTProvider");
// Check they are valid
if (getData == NULL) {
printf("ERROR: unable to find 'FTGetData' function\n");
FreeLibrary(hinstLib);
//return 1;
}
if (getDllVersion == NULL){
printf("ERROR: unable to find 'FTGetDllVersion' function\n");
FreeLibrary(hinstLib);
//return 1;
}
if (reportID == NULL){
printf("ERROR: unable to find 'FTReportID' function\n");
FreeLibrary(hinstLib);
//return 1;
}
if (reportID == NULL){
printf("ERROR: unable to find 'FTProvider' function\n");
FreeLibrary(hinstLib);
//return 1;
}
// Print the address of each function
printf("FTGetData is at address: 0x%x\n",getData);
printf("FTGetDllVersion is at address: 0x%x\n",getDllVersion);
printf("FTReportID is at address: 0x%x\n",reportID);
printf("FTProvider is at address: 0x%x\n",provider);
// Call each function and display result
pDllVersion = getDllVersion();
printf("Dll Version: %s\n", pDllVersion);
pProvider = provider();
printf("Provider: %s\n", pProvider);
reportID(name); //not sure what this does - I guess it tells the dll that I am using it.
system("pause"); //wait till keyboard is pressed before entering main loop
while( kbhit() != 1)
{
//system("cls"); //clear screen
if (getData(pData))
{
printf("Provider: %s\n", pProvider);
printf("Record ID: %d\n" , data.dataID);
printf("Yaw: %5.2f\n" , data.yaw );
printf("Pitch: %5.2f\n" , data.pitch );
printf("Roll: %5.2f\n" , data.roll );
printf("X: %5.2f\n" , data.x );
printf("Y: %5.2f\n" , data.y );
printf("Z: %5.2f\n" , data.z );
}
else
{
printf("Nothing returned from getData\n");
break;
}
}
// Unload DLL file
FreeLibrary(hinstLib);
return 0;
}

Answer 1

You told printf that yaw was a C-style string, but it's a float!

Answer 2

I think this might be caused by the structure definition of FreeTrackData.
I found an updated one from this post, and hope that would help.