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How can I pass an object of a C++ class to/from a C function?

April 26, 2017class function object pass

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How can I pass an object of a C++ class to/from a C function?

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Here’s an example (for info on extern C, see the previous two FAQs). Fred.h: /* This header can be read by both C and C++ compilers */ #ifndef FRED_H #define FRED_H #ifdef __cplusplus class Fred { public: Fred(); void wilma(int); private: int a_; }; #else typedef struct Fred Fred; #endif #ifdef __cplusplus extern “C” { #endif #if defined(__STDC__) || defined(__cplusplus) extern void c_function(Fred*); /* ANSI-C prototypes */ extern Fred* cplusplus_callback_function(Fred*); #else extern void c_function(); /* K&R style */ extern Fred* cplusplus_callback_function(); #endif #ifdef __cplusplus } #endif #endif /*FRED_H*/ Fred.cpp: // This is C++ code #include “Fred.h” Fred::Fred() : a_(0) { } void Fred::wilma(int a) { } Fred* cplusplus_callback_function(Fred* fred) { fred->wilma(123); return fred; } main.cpp: // This is C++ code #include “Fred.h” int main() { Fred fred; c_function(&fred); return 0; } c-function.c: /* This is C code */ #include “Fred.h” void c_function(Fred* fred) { cplusplus