[Bug] [C-API]: build-errors of multiple declaration of global variables when including multiple "openvino.h"

[xygnal]

OpenVINO Version

Master branch

Operating System

Ubuntu 20.04 (LTS)

Device used for inference

GPU

Framework

None

Model used

No response

Issue description

I wrote the C codes of the real-time video inference using OPENVino.
I includes <openvino/c/openvino.h> in many files,
and I get the build-errors of the multiple declaration of global variables.

I found that the cause of errors. (And I have avoided the errors at my side)
Global variables in API are declared without "extern" when using C compiler.

src/bindings/c/include/openvino/c/ov_common.h,

WITH C compiler, not static library, and LINUX,

• line 36, # define OPENVINO_C_API_EXTERN
• line 56, # define OPENVINO_C_VAR(...) OPENVINO_C_API_EXTERN attribute((visibility("default"))) VA_ARGS

WITH C compiler, global variables in API shall be defined with "extern".
So, how about modifying the ov_common.h like the below?

#ifdef __cplusplus
#define OPENVINO_C_VAR_EXTERN extern "C"
#else
#define OPENVINO_C_VAR_EXTERN extern
#endif
...
#define OPENVINO_C_VAR(...) OPENVINO_C_VAR_EXTERN ... ... ...

Step-by-step reproduction

No response

Relevant log output

Issue submission checklist

• I'm reporting an issue. It's not a question.
• I checked the problem with the documentation, FAQ, open issues, Stack Overflow, etc., and have not found a solution.
• There is reproducer code and related data files such as images, videos, models, etc.

[praasz]

@xygnal Thank you for reporting the issue and suggestion.

Here is a fix:

• [C-API] Add extern to C API symbols to solve linker issue using C compiler #28877