Simple example of getting a function pointer to an Objective-C method and calling it

FunctionPointerFromMethod.m

// To compile and test this from the command line:
//
// $> clang FunctionPointerFromMethod.m -ObjC -framework Foundation -fobjc-arc
// $> ./a.out

#import <Foundation/Foundation.h>

@interface MyClass : NSObject
- (void)someMethodThatTakesOneStringArgument:(NSString *)string;
@end

@implementation MyClass

- (void)someMethodThatTakesOneStringArgument:(NSString *)string
{
    NSLog(@"Here's the string: %@", string);
}

@end

int main(int argc, char *argv[]) {
    @autoreleasepool {
        MyClass *obj = [[MyClass alloc] init];
    
        IMP methodIMP = [obj methodForSelector:@selector(someMethodThatTakesOneStringArgument:)];
        void (*functionPointer)(id, SEL, NSString*) = (void (*)(id, SEL, NSString*))methodIMP;

        // Then call it:
        functionPointer(obj, @selector(someMethodThatTakesOneStringArgument:), @"hello");
    }
}