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No one does 
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I just did 
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Yes, not having a main method is a key part of the correct answer to that.
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You may be right, but on the other hand I can compile any code into a dll, so does a "main()" method, but still it won't execute! 
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Exactly, the correct term would be a main entry point. The main method is just a label used by compilers to indicate the main entry point of the application.
Plus, there are a few details that are different between DLLs and EXEs like the PE Header.
To alcohol! The cause of, and solution to, all of life's problems - Homer Simpson
----
Our heads are round so our thoughts can change direction - Francis Picabia
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Yes it will, if you know the magic words (or command).
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They probably saw rundll32.exe and made assumptions...
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DLL not having the main method is not the right answer.
In Windows, EXEs and DLLs have the same format which is the PE (Portable Executable) format.
The PE format has a header called the optional header which records the address of the entry point.
Both EXEs and DLLs can have an entry point.
In fact DLLs do have a default entry point called DllMain.
The only difference here is that, this entry point is optional for DLLs unlike that for an EXE.
As for a DLL having multiple entry points, an EXE can also do this the same way a DLL does, by exporting them.
And an external program can call into these exported entry points the same way it does for a DLL, using LoadLibrary and GetProcAddress.
So the real difference is in a bit in one of the PE headers which states whether the image is a DLL or not, which the loader checks before executing the image.
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The main difference is that exe runs in it's own address space as the independent process. The DLL works in the address space of the parent process, so the prolog executed during loading is different, and any entry point of the DLL cannot be called directly by OS. Only parent process can load and call DLL. That's why you need regsvr32 hosting exe to use DllRegisterServer "independent" entry point.
Regards,
Gennady
My English is permanently under construction. Be patient !!
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An EXE is an out-of-process executable.
A DLL is an in-process executable.
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Actually, you _can_ run a dll - http://support.microsoft.com/kb/164787. Agree, it's not exactly the same as running an .exe, but then again, Windows itself starts tons of processes using rundll/rundll32.
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I would set aside all the BS responses they might be looking for and tell them the basic reason. An EXE is configured by the compiler as an application and a DLL is built to be an extension library that can be shared by multiple EXE files. Nothing more technical than that is needed.
If they were looking for anything more than that at a basic level then I wouldn't want to work for them because they really like to pick nits about crap that isn't really all that relevant.
-CB
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I completely agree...
I have found in the many interviews that I have taken that when the interviewers begin asking incredibly detailed questions relating to irrelevant knowledge for most application development they have no real interest in hiring anyone. Of course, they may also just like asking people a lot of stupid questions... 
Steve Naidamast
Black Falcon Software, Inc.
blackfalconsoftware@ix.netcom.com
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Steve Naidamast wrote: I have found in the many interviews that I have taken that when the interviewers begin asking incredibly detailed questions relating to irrelevant knowledge for most application development they have no real interest in hiring anyone. Of course, they may also just like asking people a lot of stupid questions...
When they get like that I begin to realize that they're just playing "Jeopardy". Any "propeller-head" can spout out technology terms. What I want to demonstrate to a prospective employer/client is that I know how to THINK. Sure, some built-in knowledge is important but EQUALLY important is realizing you can't keep it all in your head. That's what reference material is for. Why bother memorizing everything? If I'm aware of how a particular language feature works that's enough: when I need it I'll look it up if it isn't something I use on a day-by-day basis.
I remember for a while some of the guys at our company were all about getting "certifications". Cool, except when I would go to them with a real problem they couldn't think clearly enough to solve the problem: it wasn't one of the test questions so they didn't know what to do!
Heh ...
-cb
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If i asked this question i would expect this answer:
"Both CAN be run, usually a DLL is intended to be used inside another program, that's why normally you don't run a dll directly."
But an acceptable answer will be:
"DLLs are intended to be used inside programs, while EXEs are programs themselves"
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Also, a DLL doesn't have its own stack, by default. An exe does.
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On Windows, there are cases where you can run a function in a dll with rundll32.exe if the function's takes no args and its return type is void. In other words, the function needs to be as much of a standalone as an exe file. For example, in Powersell,
PS> rundll32.exe advapi32.dll,ProcessIdleTasks
PS> rundll32.exe user32.dll,LockWorkStation
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No, they can take args using similar parameters to what WinMain() does. Just that some functions don't use them.
void CALLBACK
EntryPoint(HWND hwnd, HINSTANCE hinst, LPSTR lpszCmdLine, int nCmdShow);
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How would you use rundll32.exe to run that function then?
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I confess I didn't read the tag line either. There's a bit of a problem with the semantics of the statement too. I'd agree that you can't start an execution from a dll (from other comments, I'd be wrong about that too, but don't know how), but you definitely do run dll code.
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Well.. technically, if it is the right kind of DLL, you can.. using rundll32.exe (which has been included in at least the last few versions of windows). It lets you execute any entry-point style (think WinMain signature) named code symbol.
I guess it was easier for M$ to write a few DLL's with many functions, rather than dozens (or hundreds/thousands) of individual linked EXE's, each for a specific purpose.
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rundll32.exe, although there are no guarantees that it will work (depending on the DLL's entry points)
--
Kein Mitleid Für Die Mehrheit
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While browsing through Q&A this morning I came across this question:
FetalExecutionEngineError On OpenFileDialog.showDialog()
I'm guessing that the engine must be a little underdeveloped to get this type of error.
I wasn't, now I am, then I won't be anymore.
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What an abortion!
Ideological Purity is no substitute for being able to stick your thumb down a pipe to stop the water
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