Hi,
okay. It's not very clear for me - if I understand it correctly - you have project based on SDK (which is C only) and some part written by you in C++, correct? Technically Convert C/C++ adds C++ toolchain in C project:

the __cplusplus definition is valid for .cpp sources. So - if you have .cpp source you can use #ifdef __cplusplus - like on my hybrid testing project with main.cpp and .c SDK sources:

Anyway - what is your use case for mixing C/C++ ?
BR,
Jiri