low-level objc runtime apis

.gitignore

*
!*.m
!Makefile

array.m

// To compile: gcc -o array array.m -lobjc -framework Foundation

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

int main() {

  void *sdl_library = dlopen("/System/Library/Frameworks/Foundation.framework/Versions/Current/Foundation", RTLD_LAZY);
  if (sdl_library == NULL) {
    printf("Got dlopen error!\n");
  } else {
    printf("dlopen successful!\n");

    // Set up an NSAutoreleasePool
    Class nsautoreleasepool = objc_getClass("NSAutoreleasePool");
    id pool = class_createInstance(nsautoreleasepool, 0);
    SEL initSel = sel_registerName("init");
    id poolAfterInit = objc_msgSend(pool, initSel);

    // Create an NSMutableArray
    Class nsmutablearray = objc_getClass("NSMutableArray");

    // Regular way to create an NSMutableArray,
    // equivalent to [[NSMutableArray alloc] initWithCapacity: 10]
    id array = objc_msgSend(nsmutablearray, sel_registerName("alloc"));
    id arrayAfterInit = objc_msgSend(array, sel_registerName("initWithCapacity:"), 10);

    // Alternative, shorthand way of creating an NSMutableArray,
    // equivalent to [NSMutableArray arrayWithCapacity: 10]
    //id arrayAfterInit = objc_msgSend(nsmutablearray, sel_registerName("arrayWithCapacity:"), 10);

    // Add an NSString and the nsma class reference to the array
    objc_msgSend(arrayAfterInit, sel_registerName("addObject:"), @"test");
    objc_msgSend(arrayAfterInit, sel_registerName("addObject:"), nsmutablearray);

    // Print out the length and debug printout
    NSLog(@"%d", objc_msgSend(arrayAfterInit, sel_registerName("count")));
    NSLog(@"%@", arrayAfterInit);
  }

  return 0;
}

hello.m

// To compile: gcc -o hello hello.m -lobjc

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

int main() {

  void *sdl_library = dlopen("/System/Library/Frameworks/Foundation.framework/Versions/Current/Foundation", RTLD_LAZY);
  if (sdl_library == NULL) {
    printf("Got dlopen error!\n");
  } else {
    printf("dlopen successful!\n");

    // Set up an NSAutoreleasePool
    Class nsautoreleasepool = objc_getClass("NSAutoreleasePool");
    id pool = class_createInstance(nsautoreleasepool, 0);
    SEL initSel = sel_registerName("init");
    id poolAfterInit = objc_msgSend(pool, initSel);

    // Set up a NSString with the contents "Hello World" from a C string
    Class nsstring = objc_getClass("NSString");
    SEL stringUTF8sel = sel_registerName("stringWithUTF8String:");
    id hello = objc_msgSend(nsstring, stringUTF8sel, "Hello World\n");

    // Print it back out as a C string
    printf("%s", (char *)objc_msgSend(hello, sel_registerName("UTF8String")));
  }

  return 0;
}

Makefile

# using CXXFLAGS for Obj-C is *really* weird
CC = gcc
CXXFLAGS = -lobjc -framework Foundation
FILES = hello.m array.m

.PHONY: all
all: hello array

%: %.m
	$(CC) $(CXXFLAGS) -o $@ $<

.PHONY: clean
clean:
	rm -f hello array