API Question #define ORBITER_MODULE, C2440 error

[n72.75]

I've been bitten by the addon dev bug again recently and I'm getting back into the Orbiter API and C++.

I'm having trouble with the very simple bit of code below.

#define STRICT
#define ORBITER_MODULE

#include <OrbiterSDK.h>

DLLCLBK void opcPreStep(double simt, double simdt, double mjd)
{
	sprintf(oapiDebugString(), "%.10f", oapiGetSimStep());
}

The compiler gives me this error:

1>------ Build started: Project: Moth, Configuration: Debug Win32 ------
1>moth.cpp
1>c:\orbiter\orbiter2016\orbitersdk\include\orbiterapi.h(7227): error C2440: 'return': cannot convert from 'const char [12]' to 'char *'
1>c:\orbiter\orbiter2016\orbitersdk\include\orbiterapi.h(7227): note: Conversion from string literal loses const qualifier (see /Zc:strictStrings)
1>Done building project "Moth.vcxproj" -- FAILED.
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

when I try to compile it, which doesn't make sense to me.

If I remove the

#define ORBITER_MODULE

line it will compile and orbiter will load it, and it does exactly what I want.

My question is, why??

 

[LeePalmer]

Hi.

The oapiDebugString() returns 'const char [12]'.
The sprintf() bit is attempting to convert it. to *char , a char pointer type.

Try:
{
*char x;
x= oapiDebugString();
sprintf(x, "%.10f", oapiGetSimStep());
}


Cheers

 

[Urwumpe]

What happens without the "#define STRICT"?

 

[LeePalmer]

Of course, its the STRICT thats giving the error.
sprint() expects a *char type. Its not getting that type.
the conversion is done by returning the const value to x first.

 

[Urwumpe]

Of course, its the STRICT thats giving the error.
sprint() expects a *char type. Its not getting that type.
the conversion is done by returning the const value to x first.

Yes, but I think you are at the wrong line for the error.

The const char [12] is the formatted string. "%.10f" fits perfectly there (11 + \0).

oapiDebugStr() is also a fixed length buffer, but its more than 12.

---------- Post added at 13:51 ---------- Previous post was at 13:01 ----------

EDIT: Can somebody get me the lines 7217 - 7237 in "orbiterapi.h"

 

[GLS]

EDIT: Can somebody get me the lines 7217 - 7237 in "orbiterapi.h"

from line 7211 to 7230 (EOF) (file corresponding to the Orbiter 2016 release)

inline VECTOR3 POINTERTOREF (VECTOR3 *p)
{
	VECTOR3 v;
	v.x = DBL_MAX;            // flag
	*((VECTOR3**)&v.z) = p;   // address
	v.z = 0.0;
	return v;
}

// ======================================================================
// Internal data structures
// ======================================================================

#ifdef ORBITER_MODULE
void dummy();
void calldummy () { dummy(); }
DLLCLBK char *ModuleDate () { return __DATE__; }
#endif

#endif // !__ORBITERAPI_H

and for the Orbiter BETA version, from line 7207 to 7233

/**
 * \ingroup vec
 * \brief Construct a rotation matrix from an axis and an angle
 * \param axis rotation axis direction (must be normalised)
 * \param angle rotation angle [rad]
 * \return rotation matrix
 */
inline MATRIX3 rotm (const VECTOR3 &axis, double angle)
{
	double c = cos(angle), s = sin(angle);
	double t = 1-c, x = axis.x, y = axis.y, z = axis.z;

	return _M(t*x*x+c, t*x*y-z*s, t*x*z+y*s,
		      t*x*y+z*s, t*y*y+c, t*y*z-x*s,
			  t*x*z-y*s, t*y*z+x*s, t*z*z+c);
}

inline VECTOR4 _V(double x, double y, double z, double w)
{
	VECTOR4 vec = {x,y,z,w}; return vec;
}

inline VECTOR4 _V(const VECTOR3 &v)
{
	VECTOR4 vec = {v.x, v.y, v.z, 1.0};
	return vec;
}

 

[Urwumpe]

So the ModuleDate() function collides with STRICT because ___DATE___ is a constant string literal.

 

[martins]

I realise that ModuleDate() should return a const char*, but if I change that it will probably break every single addon.

What about a dirty hack of casting away the const from __DATE__?

return (char*)__DATE__;

Would that even compile? Would it get rid of the error? Is it too nasty to contemplate?

 

[Urwumpe]

Well, one option would be using a "const_cast<char*>(__DATE__)" there.

Since the data referenced by ModuleDate() is never overwritten, it should work without side effects.

Cleanest solution:

char* ModuleDate() {
    static char buffer[64];
    strcpy(buffer, __DATE__);
    return buffer;
}

But likely also the most inefficient one.

 

[Face]

The strange thing is: I used those defines and oapiDebugString-call just recently for the sound bridge code and got no compiler error at all. This is with Visual Studio 2015. Is the OP perhaps using a different compiler? Or beta versions of the libs?

 

[GLS]

Just checked and SSU has "#define STRICT 1", while the OP has "#define STRICT"...

 

[Face]

I can reproduce the problem if I add the compiler option "/Zc:strictStrings" to the project, just as described in the MSDN help for error C2440:

1>S:\Development\Orbiter2016\Orbitersdk\include\OrbiterAPI.h(7227): error C2440: 'return': cannot convert from 'const char [12]' to 'char *'

 

[n72.75]

The strange thing is: I used those defines and oapiDebugString-call just recently for the sound bridge code and got no compiler error at all. This is with Visual Studio 2015. Is the OP perhaps using a different compiler? Or beta versions of the libs?

VS2017, and the standard 2016 release version of orbiterapi.

 

[Face]

VS2017, and the standard 2016 release version of orbiterapi.

So perhaps 2017 is adding the above mentioned check automatically, and you have to set a switch that deactivates it.

 

[n72.75]

So perhaps 2017 is adding the above mentioned check automatically, and you have to set a switch that deactivates it.

I'll poke around when I get home tonight.

---------- Post added at 06:50 PM ---------- Previous post was at 11:42 AM ----------

Yeah, adding: "/Zc:strictStrings-" option fixes the error.

 

[n72.75]

So this is still a thing. It's always fun searching for an answer and finding your own thread, lol.