Re: registerRecordDeviceDriver.obj unresolved external symbols

["Johnson, Andrew N. via Tech-talk" <tech-talk@aps.anl.gov>]

Hi Patrick,

On 5/23/19 9:51 AM, Thomas, Patrick via Tech-talk wrote:

I think the attached is a minimum working example. Compiling it gives the following:

<snip>

link -nologo  -LTCG -incremental:no -opt:ref -release  -MACHINE:X64              -out:ads.exe        ads_registerRecordDeviceDriver.obj adsMain.obj     ..\\..\\..\\lib\\windows-x64\\adsSupport.lib  C:\\Users\\patrick.thomas\\Desktop\\epics\\base-3.14.12.8\\lib\\windows-x64\\recIoc.lib  C:\\Users\\patrick.thomas\\Desktop\\epics\\base-3.14.12.8\\lib\\windows-x64\\softDevIoc.lib  C:\\Users\\patrick.thomas\\Desktop\\epics\\base-3.14.12.8\\lib\\windows-x64\\miscIoc.lib  C:\\Users\\patrick.thomas\\Desktop\\epics\\base-3.14.12.8\\lib\\windows-x64\\rsrvIoc.lib  C:\\Users\\patrick.thomas\\Desktop\\epics\\base-3.14.12.8\\lib\\windows-x64\\dbtoolsIoc.lib  C:\\Users\\patrick.thomas\\Desktop\\epics\\base-3.14.12.8\\lib\\windows-x64\\asIoc.lib  C:\\Users\\patrick.thomas\\Desktop\\epics\\base-3.14.12.8\\lib\\windows-x64\\dbIoc.lib  C:\\Users\\patrick.thomas\\Desktop\\epics\\base-3.14.12.8\\lib\\windows-x64\\registryIoc.lib  C:\\Users\\patrick.thomas\\Desktop\\epics\\base-3.14.12.8\\lib\\windows-x64\\dbStaticIoc.lib  C:\\Users\\patrick.thomas\\Desktop\\epics\\base-3.14.12.8\\lib\\windows-x64\\ca.lib  C:\\Users\\patrick.thomas\\Desktop\\epics\\base-3.14.12.8\\lib\\windows-x64\\Com.lib
ads_registerRecordDeviceDriver.obj : error LNK2001: unresolved external symbol __imp_pvar_dset_bi_DevSet
ads_registerRecordDeviceDriver.obj : error LNK2001: unresolved external symbol __imp_pvar_func_devADSRegistrar
ads.exe : fatal error LNK1120: 2 unresolved externals

Okay, looking at your devADS.cpp file, firstly the epicsExport.h header should only be included after all the other EPICS Base headers you include. For static builds the order doesn't really matter, but it definitely will if you're building or linking to DLLs, so best keep it in the right place — it actually marks the boundary between headers for external libraries, and those for routines that will appear in the same DLL as the objects compiled from this file.

Mark Rivers was correct about the need for an extern "C" { ... } wrapper, which must appear around the epicsExportAddress() statements and any other epicsExport* statements you include in a C++ source. That change is sufficient for me to be able to build your example — the routines and data structures themselves don't have to be marked as extern "C".

The second error above is there because you still have a registrar entry for devADSRegistrar in the adsSupport.dbd file.

HTH,

- Andrew

-- 
Complexity comes for free, Simplicity you have to work for.