pseudo variable

Can someone please explain me what is a Pseudo Variable and what exactly is the first parameter to the function WinMain below??

Code:

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GetStartupInfo(&StartupInfo);
int nMainRetVal = WinMain((HINSTANCE)&__ImageBase, NULL, pszCommandLineAnsi,
  (StartupInfo.dwFlags & STARTF_USESHOWWINDOW)
      ? StartupInfo.wShowWindow : SW_SHOWDEFAULT);

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Also what does the following statement do??

Code:

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extern "C" const IMAGE_DOS_HEADER __ImageBase;

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Quote:

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what is a Pseudo Variable

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That's not a generally used term, so you would have to explain the context of your question.
Given the other question, I assume you refer to __ImageBase as a pseudo variable, so let me explain what that is.

Basically, __ImageBase is a magic variable name that is recognized by the compiler/linker/loader and replaced by something special. That special thing is your program as it is loaded into memory. Thus, &__ImageBase (taking the address) gets the base address where your module (the .exe or .dll) was loaded, which happens to be exactly what the HINSTANCE handle is as well. This handle is primarily used to load resources from that particular module.