extern “C” DLL: Debug is OK, Release throws Error C2059

5
votes

I've got a DLL that I've created as a C++ Win32 application. To prevent name mangling in my DLL, I have used the EXPORT definition defined below:

#ifndef EXPORT
#define EXPORT extern "C" __declspec(dllexport)
#endif

EXPORT int _stdcall SteadyFor(double Par[], double Inlet[], double Outlet[]);

To get this code to compile, I had to go into the project's Properties and set the C/C++ Calling Convention to __stdcall (/Gz) and set Compile As to Compile as C++ Code (/TP).

This worked in Debug mode, but Release mode is throwing error C2059: syntax error: 'string' on all of my EXPORT functions - even though I have configured the Release mode settings to be the same as the Debug settings.

How do I get Release Mode to compile?

Regards,
~Joe
(Developing under Visual Studio 2008 Professional)

EDIT:
A lot of comments about my #define, which does not appear to be causing any problems.

To eliminate the confusion, my header file has been rewritten as follows:

#ifndef coilmodel_h
#define coilmodel_h

extern "C" __declspec(dllexport) int _stdcall steadyFor(double Par[], double Inlet[], double Outlet[], char* FileIn, char* FileOut);

#endif

That is all of it.

The error is:
Description error C2059: syntax error: 'string'
File coilmodel.h
Line 4

Again, this error only appears in Release mode, not Debug mode.
Project is a C++ Win32 DLL application.

4
c++dllextern
I think the code you posted is not relevant to the problem. Can you tell us which line chokes as well as post the code for that line. From the code you posted it looks like you do not have EXPORT defined in Release mode. – Romain Hippeau
See my "Edit" section above. I wasn't able to explain it all here. – jp2code

4 Answers

8
votes

If your source file has a .c extension, the compiler you are using will compile it as C (not C++) and produce that error on the extern "C". If that is the case, then you need to use the /TP switch as you already noted or rename the file to .cpp. The other solution is to put #ifdefs around the extern:

#ifdef __cplusplus
extern "C"
#endif
2
votes

I would guess EXPORT is defined as something else in Release builds. Since you've got an #ifndef around your definition, that won't do anything if it is already defined, then you get something else (maybe a string?) pasted at the beginning of your function declarations.

So maybe try something like this:

#ifdef EXPORT
    #error EXPORT already defined!
#else
    #define EXPORT extern "C" __declspec(dllexport)
#endif
1
votes

Forcing Compile As to Compile as C++ Code (/TP) - did you set this on all build configurations - debug/release x 32/x64 etc. I avoid using this option, much easier to name the file appropriately for the compiler to choose automatically.

You only need the "C" part of extern "C" if the file is C++ to turn off the name mangling.

I prefer to arrange the shared public header using this format, so you can include in C/C++ internally or externally.

#ifdef __cplusplus
# define NOMANGLE extern "C"
#else
# define NOMANGLE
#endif

#ifdef EXPORT_BUILD
# define EXPORT NOMANGLE __declspec(dllexport)
#else
# define EXPORT NOMANGLE __declspec(dllimport)
#endif
0
votes

Unprobable, but make sure dllexport or _stdcall is not #defined...