Linking C++ code to C in Borland C++ 3.1 compiler - c

Question

Part of my FYP is to write code for a very old game(Wolfenstein-3D). It requires the use of the Borland C++ v3.1 compiler. This is the code I currently have but it's giving an error in the Borland compiler. Any ideas?
Error In Compiler:
Neuron.h
#ifdef __cplusplus // only actually define the class if this is C++
class Neuron {
public:
void foo();
int bar(int x, int y);
};
#else // C doesn't know about classes, just say it's a struct
typedef struct Neuron Neuron;
#endif
// access functions
#ifdef __cplusplus
#define EXPORT_C extern "C"
#else
#define EXPORT_C
#endif
EXPORT_C Neuron* NeuronNew(void);
EXPORT_C void NeuronDelete(Neuron* n);
EXPORT_C void NeuronFoo(Neuron* n);
EXPORT_C int NeuronBar(Neuron* n, int x, int y);
Neuron.cpp
#include "NEURON.h"
void Neuron::foo() {
}
int Neuron::bar(int x, int y) {
return x+y;
}
EXPORT_C Neuron* NeuronNew(void) {
return new Neuron();
}
EXPORT_C void NeuronDelete(Neuron* n) {
delete n;
}
EXPORT_C void NeuronFoo(Neuron* n) {
return n->foo();
}
EXPORT_C int NeuronBar(Neuron* n, int x, int y) {
return n->bar(x, y);
}
Usage in C source file
#include "NEURON.h"
...
void GameLoop (void)
{
...
Neuron* m = NeuronNew();
NeuronFoo(m);
NeuronDelete(m);
...
}
My assumption is that even though the compiler is a C++ compiler there's something 'new' in the C++ code that the compiler can't handle

Answer 1

The error message looks very much like the one you get from other compilers when they can't build the .cpp file for your class. It's not complaining about NeuronNew, but about _Neuron_new (note lowercase 'n' and extra underscore), so that's likely what Borland names the constructor/destructor?
Is it successfully compiling the .cpp and as C++? Is the file suffix mapping hooked up for those in the compiler? Have you added invalid code to the #ifdef __cplusplus line to verify that is ever defined, and not always defined (as 0 or 1)? Are you using the same case for all includes, file names and in the Makefile/project so they can be found?
Oh, have you tried doing:
typedef struct Neuron* NeuronPtr;
and then using NeuronPtr instead of Neuron* in the C wrapper? C++ Compiler shouldn't care (as long as you do a typedef class Neuron* NeuronPtr; in the __cplusplus part), but it means that it might no longer try to resolve the forward-declared struct in any C code.