How to access iOS photo library / use Objective-C properly?

Hi,
It’s my first project working for iOS with UE4(4.17.2) - I see your code and dude, thank you for the clear explanation. However there is a detail is not that clear to me: Can I just write this code block inside a C++ function?
#if PLATFORM_IOS
NSLog(@“Show image picker”);
[MyViewController runSelectPhoto];
#endif
So far, I compiled the class and it was successful, but I was wondering about how to call the functions wrote with ObjectiveC