I am assuming that you are looking to include existing C++ code in Simulink. There are three ways which allows you to integrate C++ code into Simulink:
1) You can integrate existing C (or C++) functions, such as device drivers, lookup tables, and general functions and interfaces, into Simulink models by using the Legacy Code Tool. Please refer to the following documentation for more information:
2) You can manually write a wrapper S-function to call external C++ code. The procedure is very similar to writing a wrapper function in C. Please refer to the following doc page:
3) Another option is to use Stateflow custom code interface. You may refer to the following documentation:
There is also an example available demonstrating how to use Stateflow to integrate external code into a model:
