How Can C Libraries Be Effectively Interfaced with C Code?

Interfacing C Libraries with C Code

Extending C library functionality to support C function calls allows seamless integration between C and C code. While it is technically feasible, there are certain considerations and techniques that must be taken into account for successful interfacing.

Creating the Interface Layer

To expose C functions to C code, an interface layer must be created in C . This layer will declare functions with the "extern 'C'" specifier, essentially making them C functions. For instance:

extern "C" int foo(char *bar)
{
    return realFoo(std::string(bar));
}

Here, foo() is the C function that calls the C function realFoo() when invoked from a C module.

Gotchas and Considerations

C Identifiers in C Code: Ensure that C identifiers used in interface functions are valid in C.

Enum Size Differences: Note that enum size can vary between C and C compilers.

Struct Handling: To avoid confusion in C, typedef structs with the following syntax:

typedef struct X { ... } X

Pointers for C Objects: Pass C objects using pointers declared in C as struct X, where X is the C object.

Resources and Documentation

• Header wrapping: https://www.genivia.com/doc/cpp/cpp_index.html
• C API for C: https://www.apriorit.com/our-expertise/ai-machine-learning
• PIMPL principle: https://www.codeproject.com/Articles/738906/Cplusplus-Pointer-to-Implementation-PIMPL-Idiom

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