DLL causes program to crash only when memory is allocated - c++

Question

I am writing a small DLL, which once injected into my target process, will find a hwnd and write the window's text to a file. I have it setup like this:
hWnd = FindWindow(L"tSkMainForm",NULL);
chat = FindWindowEx(hWnd, NULL, L"TConversationForm", NULL);
ofstream myfile("X:\\Handles.txt", ios::out | ios::app);
if (myfile.is_open())
{
int len;
len = SendMessage(chat, WM_GETTEXTLENGTH, 0, 0) + 1; // + 1 is for the null term.
char* buffer = new char[len];
SendMessageW(chat, WM_GETTEXT, (WPARAM)len, (LPARAM)buffer);
myfile.write(buffer,len); /* << buffer <<endl; */
myfile.close();
delete[] buffer;
}
It works for a seemingly random amount of time, then the application (Skype) crashes. It only crashes when I allocate memory. I have tried using malloc with:
char* buffer = (char*)malloc(len); //I even tried removing "(char*) before malloc
//Do the rest of the stuff here
free((void*) buffer);
But that crashes too.
My DLL calls CreateThread, adds an extra menu item via AppendMenu, and handles the messages for it, all perfectly. It just seems that allocating memory doesn't want to work, but only at random times. I am not sure, but I think Skype is overwriting my memory, or I am overwriting Skype's memory (how would I ensure that the two don't overwrite each other then?)
Also, I know an API exists for Skype, but I want to do it this way. I would use the Skype API if I wanted to write a serious program.
Thanks.

Answer 1

Of course it crashes. "Injecting a DLL in another process" is something you shouldn't be doing in the first place, and certainly not if you cannot figure this out.
Your problem is that your DLL makes assumptions about the environment it's running in. In particular, you assume there's a C++ heap (or a C heap, for malloc), and that is has precisely the right state for your program. That's just not the case. Normal C++ rules do not apply to injected DLL's; your DLL must be able to stand on its own legs.