In the world of cross-platform, it is common for the need to create bridges of communication between different languages. While working with React Native and iOS, I stumbled on a need to interop with a C++ class. This post covers how you can communicate between Objective-C and C++ code.

Using Objective-C++

You can transform your Objective-C file (.m) to Objective-C++ (.mm). This by default enables you to call any C++ code in your Objective-C++ file.

MyObjective_c_file.mm

#include "SomePrivateCppClass.h" @implementation MyObjective_c_file - (instancetype) init { // Add your logic here SomePrivateCppClass::someMethod(); } @end 

Note - Sometimes you can have issues with this approach especially when your C++ interface is importing code that causes an issue for the Objective-C compiler. To overcome this you can do the next step

Interopping with a C interface to call an Objective-C function from C++

When file separation is required due to external dependencies. You can interop by using a C interface.

C.interface.h

void callFromCpp(const char *dataPayload); 

MyObjective_c_file.mm

 @implementation MyObjective_c_file ... - (void)myMethod: (NSString *) dataPayload { // Your logic here } @end void callFromCpp(const char *dataPayload) { NSString *convertedString = [[NSString alloc] initWithCString: dataPayload encoding:NSUTF8StringEncoding]; MyObjective_c_file myInstance = [[MyObjective_c_file alloc] init]; [MyObjective_c_file myMethod: convertedString]; } 

YourCppClass.cpp

YourCppClass::WhatEverMethod() { callFromCpp(stringData.c_str()); } 

Passing pointers with a C interface to call a C++ method.

When using a C interface, you can also pass a pointer of your C++ class in order to call it from your Objective-C++ code (This is ideal when you can't include your C++ file due to dependencies).

In this case, you will instantiate your Objective-C class by calling a C function from your C++ method, then pass a pointer of your C++ class to your Objective-C interface for it to consume it.

C.interface.h

void initFromCpp(long castBridgePointer); 

MyObjective_c_file.mm

#include "YourCppClass.h" @implementation MyObjective_c_file static YourCppClass *pointerToBridge; ... - (void)storeCastBridgePointer: (long) ptr { pointerToBridge = (YourCppClass *) ptr; } @end void initFromCpp(long castBridgePointer) { MyObjective_c_file myInstance = [[MyObjective_c_file alloc] init]; [myInstance storeCastBridgePointer: castBridgePointer]; } 

YourCppClass.cpp

YourCppClass::YourCppClass() { // whatever logic... initFromCpp((long) this); } 

Conclusion

Interop between C++ and Objective-C is not too complicated. The purpose of this post is to bring both solutions, the plain Objective-C approach and C interface approach, into a single post where anyone can reference in the future