Re: CString Format causes memory issue
Jen" <leonard522@aol.com> wrote in message
news:1156812269.733994.133260@74g2000cwt.googlegroups.com...
Okay...I figured out how to set compiler / linker options and was able
to debug the code. I found the line it crashes on.
I am using an extension DLL, and it crashes on a function call to the
DLL. FYI, I have to link to MFC Statically because of the extension
dll.
That's your problem, Jen. Extension DLL's need to have MFC dynamically
linked, not statically linked.
The issue is with static linking, there are two heap managers, one for the
..exe and one for the .dll. These two heaps don't know anything about each
other. The .exe passes a CString to the dll. The DLL assigns the CString
to something else. This causes the internal memory (call it 'buf') of
CString to be reallocated (the old buffer is tossed, and a new one is
allocated). When the old is tossed, it does a free(buf). This uses the
DLL's heap manager to free it. But buf was initially allocated in the .exe,
with the .exe's heap manager. So, freeing memory allocated by an
incompatible heap manager yields CRASH!
The short of it is, your Extension Dll MUST BE DYANMICALLY LINKED if you
want to pass MFC objects like CString from the .exe. This causes only one
heap manager to be used, avoiding the incompatiblity.
BTW, it is documented that MFC Extension DLL's must be dynamically linked.
-- David
http://www.dcsoft.com
Here is the code:
CString titleStr;
GetProfileGraphTitle(2,titleStr); //Crashes here!
CString GraphTitle = titleStr.GetBuffer(0);
The function is in my DLL. Here is the prototype and function:
__declspec(dllexport) void GetProfileGraphTitle(int num,CString &str);
void GetProfileGraphTitle(int num,CString &str) {
if(num >= 0) str = ProfileGraphs[num].GraphTitle;
}
The ProfileGraphs variable is a structure defined as follows:
ProfileGraphData ProfileGraphs[NUM_PROFILE_GRAPHS];
struct ProfileGraphData {
CString GraphTitle;
CString ShortTitle;
BOOL IsSelected;
int Xunits; //type of X units
int Yunits; //type of Y units - in user defined graphs this is the
units selected by the user
int NumCurves;
int NumPoints;
DynamicCurve theData[MAX_PROFILE_CURVES];
float MaxY;
float MinY;
float UserMaxY;
float UserMinY;
BOOL UseDefaults;
float IgnoreLimit;
int StartAvg;
int EndAvg;
//only for user defined graphs
int GraphType[MAX_PROFILE_CURVES];
int ParamType;
int CurveNum[MAX_PROFILE_CURVES];
int FileYUnits;
int ParamNumber;
};
#define MAX_PROFILE_CURVES 50
#define NUM_PROFILE_GRAPHS 50
Is there anything that you can think of that may be wrong? Or a place
to start? Thanks!!
Jen