C++ std::string Parameter is <Bad Ptr> - c++

Question

I'm using Visual Studio 2010.
I have a class with the following constructor:
CVideoAnnotation::CVideoAnnotation(std::string aPort, DWORD aBaudRate)
I create an instance of CVideoAnnotation as follows:
CVideoAnnotation cVideoAnnotation("COM3", CBR_9600);
'CBR_9600' is a macro that resolves to 9600.
Down in the constructor, aBaudRate is 9600 as expected. However, aPort does not get passed properly. When I hover the cursor over it, IntelliSense gives a value of <Bad Ptr>.
Does anybody have any thoughts on why the string does not pass properly?
Thanks,
Dave
As an update to my original question, I'm adding the assembly code for the constructor call and the population of locals once inside the constructor.
CVideoAnnotation cVideoAnnotation("COM3", CBR_9600);
0041177D push 2580h
00411782 sub esp,20h
00411785 mov ecx,esp
00411787 mov dword ptr [ebp-174h],esp
0041178D push offset string "COM3" (4198C8h)
00411792 call std::basic_string<char,std::char_traits<char>,std::allocator<char> >::basic_string<char,std::char_traits<char>,std::allocator<char> > (41131Bh)
00411797 mov dword ptr [ebp-17Ch],eax
0041179D lea ecx,[ebp-11h]
004117A0 call dword ptr [__imp_CVideoAnnotation::CVideoAnnotation (41D4DCh)]
004117A6 mov dword ptr [ebp-180h],eax
004117AC mov dword ptr [ebp-4],0
CVideoAnnotation::CVideoAnnotation(std::string aPort, DWORD aBaudRate)
{
100137F0 push ebp
100137F1 mov ebp,esp
100137F3 push 0FFFFFFFFh
100137F5 push offset __ehhandler$??0CVideoAnnotation##QAE#V?$basic_string#DU?$char_traits#D#std##V?$allocator#D#2##std##K#Z (1001DC82h)
100137FA mov eax,dword ptr fs:[00000000h]
10013800 push eax
10013801 sub esp,164h
10013807 push ebx
10013808 push esi
10013809 push edi
1001380A push ecx
1001380B lea edi,[ebp-170h]
10013811 mov ecx,59h
10013816 mov eax,0CCCCCCCCh
1001381B rep stos dword ptr es:[edi]
1001381D pop ecx
1001381E mov eax,dword ptr [___security_cookie (10026090h)]
10013823 xor eax,ebp
10013825 mov dword ptr [ebp-10h],eax
10013828 push eax
10013829 lea eax,[ebp-0Ch]
1001382C mov dword ptr fs:[00000000h],eax
10013832 mov dword ptr [ebp-18h],ecx
10013835 mov dword ptr [ebp-84h],0
1001383F mov dword ptr [ebp-4],0

Answer 1

If you are implementing CVideoAnnotation in a separate DLL then you are having a well know issue of crossing DLL boundaries when using STL containers. To verify that this is the case create a new constructor taking a const char* instead of std::string and try..
Another thing, instead of std::string prefer to use const std::string&

Answer 2

Passing string to and from DLLs should work just fine. As noted above using STL containers in this way can be problematic but string is fine.
Do you have any evidence beyond Intellisense that the string is messed up? In Release builds Intelliesnse can be sketchy. Try adding cout << aPort << endl; into that constructor to make sure.
If it really is incorrect I would just debug from the caller into the constructor call - see where the string is pushed as a parameter, and see where on the stack it's picked up from for use inside the constructor. Something must be out of sync here, assuming both DLL and app use the same version of the C++ runtimes, and you should be able to tell why by inspecting the assembler code.

Answer 3

"COM3" is not a std::string it is a const char *, try creating a std::string to pass in.

Answer 4

I too was fighting what looked like bad byte alignment resulting in . Based on the suggestions here that crossing library boundaries can be problematic, I suspected (even though I am using a static library instead of DLL) that I might be dealing with the same sort of problem. I was instantiating a class in one library whose code was in another. When I moved the instantiation into the library where its code was the problem went away. I don't understand why this worked but at least I can now move forward.