main.c

#ifdef __OBJC__

// clang -framework Foundation -o ObjC -ObjC main.c

#import <Foundation/Foundation.h>

int main(int argc, const char **argv)
{
	NSString *string = [[NSString alloc] initWithUTF8String:"Objective-C"];

	const char *cstring = [string UTF8String];
	
	printf("Hello %s\n", cstring);
	
	return 0;
}

#else

// clang -framework Foundation -o C main.c

#include <objc/runtime.h>
#include <objc/message.h>
#include <stdio.h>

extern void objc_release(id object);

int main(int argc, const char **argv)
{
	Class NSStringClass = objc_getClass("NSString");
	SEL allocSelector = sel_getUid("alloc");
	SEL initWithUTF8StringSelector = sel_getUid("initWithUTF8String:");
	SEL UTF8StringSelector = sel_getUid("UTF8String");
	
	id string = objc_msgSend(objc_msgSend((id)NSStringClass, allocSelector), initWithUTF8StringSelector, "Objective-C runtime only");
	
	const char *cstring = (const char *)objc_msgSend(string, UTF8StringSelector);
	
	printf("Hello %s\n", cstring);
	
	objc_release(string);
	
	return 0;
}

#endif