How can I pass a dynamic generated C++ function as *funcprt to a C API?
The API exports this:
DllImport void api_register_func(char *func_name, void (*funcptr)(char *, char *));
I have to create the function while runtime because I don't know about it before. So I used a class:
class JsFunc
{
public:
char * JsFuncName;
char * JsParameter;
void RunFunc(char * val1, char * val2)
{
printf("\nJsFunc.runFunc executed, JsParameter=%s passed\n",JsParameter);
}
};
And call it like this:
JsFunc * jsm = new JsFunc ();
jsm->JsFuncName = external_parameter1;
jsm->JsParameter = external_parameter2;
api_register_func(external_parameter1, jsm->RunFunc);
But VisualStudio 2015 tells me:
Error C3867 'JsFunc::runFunc': non-standard syntax; use '&' to create a pointer to member VJCS C:\Users\astrauss\Source\Repos\VCJS\VCJS\VCJS.cpp 54
Sorry if the code is bad, I'm not a C/C++ programmer but need to get this running for my daily work. Thanks!
Unfortunately, you don't have very many options here. The API:
DllImport void api_register_func(char *func_name,
void (*funcptr)(char *, char *));
only lets you provide a function pointer, without any context. So you can pass in a free function or a static member function, but you have no way of providing a member function. If you had a context:
DllImport void better_api_register_func(char *func_name,
void *context,
void (*funcptr)(void *, char *, char *));
Then you could write a simple lambda:
api_register_func(external_parameter1,
jsm, //context
[](void *ctxt, char* arg1, char* arg2) {
static_cast<JsFunc*>(ctxt)->runFunc(arg1, arg2);
});
and you're effectively using a member function as the callback. However, this isn't an option. Instead, you're stuck with using a global variable:
std::unique_ptr<JsFunc> the_global_func;
Which you can allocate at runtime:
the_global_func.reset(new JsFunc);
// set stuff
And then use the global in a lambda. Since it's global, we don't need to (in fact, can't) capture it - which means our lambda can be convertible to a function pointer:
api_register_func(external_paramter1,
[](char* arg1, char* arg2) {
the_global_func->runFunc(arg1, arg2);
});