VS ATL exe template cannot generate a DLL

The error

The build reports:

EXEC : error : MIDL will not generate DLLDATA.C unless you have at least 1 interface in the main project.

And the pre-build echo looks like this:

if exist dlldata.c goto :END
echo Error: MIDL will not generate DLLDATA.C unless you have at least 1 interface in the main project.
Exit 1
:END

Debugging an ATL project late at night

How you get here

graph TB
OpenVS["Open Visual Studio"]-->NewATL["New ATL project"]
NewATL-->ChooseExe["Choose an .exe project"]
ChooseExe-->TwoProjects["You get ATLProject1 and ATLProject1PS"]
TwoProjects-->RunPS["Build ATLProject1PS"]
RunPS-->Error["The error above"]

What is actually wrong

The message sounds like you forgot an interface. A stock Visual Studio template should generate that for you, so an “interface problem” is the wrong first guess.

Look at if exist — this is a pre-build event. If dlldata.c is not next to the project that checks for it, the check fails even when MIDL already wrote the file.

The proxy/stub (PS) project has a pre-build event that tests for dlldata.c. That file does not live in the same folder as the proxy/stub .vcxproj, so the check cannot see it. Change the pre-build event for every configuration/platform so it looks in the parent (main) project folder.

Linking the proxy/stub project has the same shape of bug: the linker cannot find ATLProject1ps.def because it lives under ATLProject1.

Adjust the pre-build event and linker inputs

The fix

Step one

Point the pre-build event at the parent folder:

if exist ../ATLProject1/dlldata.c goto :END
echo Error: MIDL will not generate DLLDATA.C unless you have at least 1 interface in the main project.
Exit 1
:END

Step two

Fix the module-definition path:

graph TB
Props["Project properties"]-->Linker["Linker"]
Linker-->Input["Input"]
Input-->Def["Module definition file"]
Def-->Path["Set it to ../ATLProject1/ATLProject1PS.def"]

After both changes, the PS project can see dlldata.c and the .def file, and the MIDL error goes away.