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how_to_wrap_openvino_objects_with_c.md

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How to wrap OpenVINO objects with C

Here is the details about how to wrap objects(C++) form OpenVINO to objects(C).

In OpenVINO C++ implementation, many objects are defined with class, such as ov::Core, ov::Model, ov::InferRequest..., but for C class doesn't be supported. So, C need to create new object to represent those objects. Three kinds of methods had been adopted in our implementation:

Tips:

  1. For the objects which needs to be hided for users, C struct contains a shared pointer will be adopted.
  2. For the objects which needs to be created, operated and read by users, rewrite the C++ class will be better.
  3. For some simple objects, C struct contains a instance of C++ class will be enough.

Wrap by C++ Shared Pointer

C construct a new struct represents the class, which contains a shared pointer to the class as following:

struct ov_class_name {
    std::shared_ptr<ov::ClassName> object;
};

Here is an example (core) for wrapping by shared pointer:

https://github.com/openvinotoolkit/openvino/blob/d96c25844d6cfd5ad131539c8a0928266127b05a/src/inference/include/openvino/runtime/core.hpp#L41-L684

Represent by C struct:

https://github.com/openvinotoolkit/openvino/blob/d96c25844d6cfd5ad131539c8a0928266127b05a/src/bindings/c/src/common.h#L47-L53

C provides the struct by typedef struct ov_core ov_core_t;

Wrap by C++ Object

C construct a new struct represents the class, which contains an instance to C++ class as following:

struct ov_ClassName {
    ov::ClassName object;
};

Here is an example (layout) for wrapping by shared pointer:

https://github.com/openvinotoolkit/openvino/blob/d96c25844d6cfd5ad131539c8a0928266127b05a/src/core/include/openvino/core/layout.hpp#L44-L107

Represent by C struct:

https://github.com/openvinotoolkit/openvino/blob/d96c25844d6cfd5ad131539c8a0928266127b05a/src/bindings/c/src/common.h#L95-L101

C provides the struct by typedef struct ov_layout ov_layout_t;

Wrap by Rewrite

C construct a new struct represents the class, which rewrites related info to the class as following:

typedef struct {
    ov::ClassName object;
} ov_class_name_t;

Here is an example (shape) for wrapping by shared pointer: https://github.com/openvinotoolkit/openvino/blob/d96c25844d6cfd5ad131539c8a0928266127b05a/src/core/include/openvino/core/shape.hpp#L21-L40

Represent by C struct here

https://github.com/openvinotoolkit/openvino/blob/d96c25844d6cfd5ad131539c8a0928266127b05a/src/bindings/c/include/openvino/c/ov_shape.h#L15-L22

NOTE: this implementation needs developer create the C++ class based on the C struct info in using this rewrite type.

See also