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    <p>This technique will work in some cases where standard data types are incompatible, but in others it will fare no better: name mangling differences and class memory layout differences (vptrs and tags) come to mind.</p> <p>This is why C APIs are preferred.</p> <p>But you <em>can</em> improve usability by burying the C API where the library caller never needs to see it. Then add a thin, idiomatic C++ overlay that provides the visible library interface. In some cases the thin overlay code can be used on both caller and library side, each compiled in its own environment: flags, link conventions, etc. Only C data types are exchanged. The simpler these data types are, the more compatibility you'll obtain.</p> <p>The layer also takes care that memory allocation and deallocation occur on the same side of the API on a per object basis, as your code does. But it can be more flexible. For example, it's possible to arrange for an object allocated in the caller to be deallocated in the library and vice versa.</p> <pre><code>// library.h for both caller and library // "shadow" C API should not be used by caller extern "C" { void *make_message(char *text); char *get_text_of_message(void* msg); void send_message(void *msg); // destroys after send. } // Thin C++ overlay class Message { void *msg; public: Message(const std::string &amp;text) { msg = make_message(text.c_str()); } void send() { if (msg) send_message(msg); else error("already sent"); msg = 0; } std:string getTextString() { return std:string(get_text_of_message(void* msg)); } } </code></pre>
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    1. POC++ library API. Using converter classes instead of plain C api
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    1. CO"name mangling differences and class memory layout differences (vptrs and tags) come to mind."- I use very small subset of C++ for conversion class. It is possible to go even further and put all internal data of conversion class into aggregated POD struct member. If you need to pass deleter, it is possible to store it in POD struct as function pointer. There is no need for vtables. As the result ABI requirenments are very low. I can afford a little ABI requirenments trading-off some compatability. In any case it is better than doing tens of different builds.
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    2. CO"But you can improve usability by burying the C API where the library caller never needs to see it." - Well, I want to eliminate need for doing boilerplate code on both sides. It is tedious and error-prone to manually wrap each each function three times by hands: first at the middle - plain C, second at user side, and third at library side. Instead of this I am thinking about wrapping only some types into *Converter classes - and as the result you may use many different such types as function parameters, without need to wrap EACH such function THREE times.
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    3. COIf it would be some automatic tool for generate wrappers around each function - that will change situation, but currently I don't know such tool. Closest thing I have in mind is SWIG, but it does not do C++ <-> C++ stuff.
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