macOS Objective-C


Note that programs written in Objective-C retain their class declarations when compiled into Mach-O binaries. Such class declarations include the name and type of:
  • The class
  • The class methods
  • The class instance variables
You can get this information using class-dump:
Note that this names could be obfuscated to make the reversing of the binary more difficult.

Classes, Methods & Objects

Interface, Properties & Methods

// Declare the interface of the class
@interface MyVehicle : NSObject
// Declare the properties
@property NSString *vehicleType;
@property int numberOfWheels;
// Declare the methods
- (void)startEngine;
- (void)addWheels:(int)value;


@implementation MyVehicle : NSObject
// No need to indicate the properties, only define methods
- (void)startEngine {
NSLog(@"Engine started");
- (void)addWheels:(int)value {
self.numberOfWheels += value;

Object & Call Method

To create an instance of a class the alloc method is called which allocate memory for each property and zero those allocations. Then init is called, which initilize the properties to the required values.
// Something like this:
MyVehicle *newVehicle = [[MyVehicle alloc] init];
// Which is usually expressed as:
MyVehicle *newVehicle = [MyVehicle new];
// To call a method
// [myClassInstance nameOfTheMethodFirstParam:param1 secondParam:param2]
[newVehicle addWheels:4];

Class Methods

Class methods are defined with the plus sign (+) not the hyphen (-) that is used with instance methods. Like the NSString class method stringWithString:
+ (id)stringWithString:(NSString *)aString;

Setter & Getter

To set & get properties, you could do it with a dot notation or like if you were calling a method:
// Set
newVehicle.numberOfWheels = 2;
[newVehicle setNumberOfWheels:3];
// Get
NSLog(@"Number of wheels: %i", newVehicle.numberOfWheels);
NSLog(@"Number of wheels: %i", [newVehicle numberOfWheels]);

Instance Variables

Alternatively to setter & getter methods you can use instance variables. These variables have the same name as the properties but starting with a "_":
- (void)makeLongTruck {
_numberOfWheels = +10000;
NSLog(@"Number of wheels: %i", self.numberOfLeaves);


Protocols are set of method declarations (without properties). A class that implements a protocol implement the declared methods.
There are 2 types of methods: mandatory and optional. By default a method is mandatory (but you can also indicate it with a @required tag). To indicate that a method is optional use @optional.
@protocol myNewProtocol
- (void) method1; //mandatory
- (void) method2; //mandatory
- (void) method3; //optional

All together

// gcc -framework Foundation test_obj.m -o test_obj
#import <Foundation/Foundation.h>
@protocol myVehicleProtocol
- (void) startEngine; //mandatory
- (void) addWheels:(int)value; //mandatory
- (void) makeLongTruck; //optional
@interface MyVehicle : NSObject <myVehicleProtocol>
@property int numberOfWheels;
- (void)startEngine;
- (void)addWheels:(int)value;
- (void)makeLongTruck;
@implementation MyVehicle : NSObject
- (void)startEngine {
NSLog(@"Engine started");
- (void)addWheels:(int)value {
self.numberOfWheels += value;
- (void)makeLongTruck {
_numberOfWheels = +10000;
NSLog(@"Number of wheels: %i", self.numberOfWheels);
int main() {
MyVehicle* mySuperCar = [MyVehicle new];
[mySuperCar startEngine];
mySuperCar.numberOfWheels = 4;
NSLog(@"Number of wheels: %i", mySuperCar.numberOfWheels);
[mySuperCar setNumberOfWheels:3];
NSLog(@"Number of wheels: %i", mySuperCar.numberOfWheels);
[mySuperCar makeLongTruck];

Basic Classes


// NSString
NSString *bookTitle = @"The Catcher in the Rye";
NSString *bookAuthor = [[NSString alloc] initWithCString:"J.D. Salinger" encoding:NSUTF8StringEncoding];
NSString *bookPublicationYear = [NSString stringWithCString:"1951" encoding:NSUTF8StringEncoding];
Basic classes are immutable, so to append a string to an existing one a new NSString needs to be created.
NSString *bookDescription = [NSString stringWithFormat:@"%@ by %@ was published in %@", bookTitle, bookAuthor, bookPublicationYear];
Or you could also use a mutable string class:
NSMutableString *mutableString = [NSMutableString stringWithString:@"The book "];
[mutableString appendString:bookTitle];
[mutableString appendString:@" was written by "];
[mutableString appendString:bookAuthor];
[mutableString appendString:@" and published in "];
[mutableString appendString:bookPublicationYear];


// character literals.
NSNumber *theLetterZ = @'Z'; // equivalent to [NSNumber numberWithChar:'Z']
// integral literals.
NSNumber *fortyTwo = @42; // equivalent to [NSNumber numberWithInt:42]
NSNumber *fortyTwoUnsigned = @42U; // equivalent to [NSNumber numberWithUnsignedInt:42U]
NSNumber *fortyTwoLong = @42L; // equivalent to [NSNumber numberWithLong:42L]
NSNumber *fortyTwoLongLong = @42LL; // equivalent to [NSNumber numberWithLongLong:42LL]
// floating point literals.
NSNumber *piFloat = @3.141592654F; // equivalent to [NSNumber numberWithFloat:3.141592654F]
NSNumber *piDouble = @3.1415926535; // equivalent to [NSNumber numberWithDouble:3.1415926535]
// BOOL literals.
NSNumber *yesNumber = @YES; // equivalent to [NSNumber numberWithBool:YES]
NSNumber *noNumber = @NO; // equivalent to [NSNumber numberWithBool:NO]

Array, Sets & Dictionary

// Inmutable arrays
NSArray *colorsArray1 = [NSArray arrayWithObjects:@"red", @"green", @"blue", nil];
NSArray *colorsArray2 = @[@"yellow", @"cyan", @"magenta"];
NSArray *colorsArray3 = @[firstColor, secondColor, thirdColor];
// Mutable arrays
NSMutableArray *mutColorsArray = [NSMutableArray array];
[mutColorsArray addObject:@"red"];
[mutColorsArray addObject:@"green"];
[mutColorsArray addObject:@"blue"];
[mutColorsArray addObject:@"yellow"];
[mutColorsArray replaceObjectAtIndex:0 withObject:@"purple"];
// Inmutable Sets
NSSet *fruitsSet1 = [NSSet setWithObjects:@"apple", @"banana", @"orange", nil];
NSSet *fruitsSet2 = [NSSet setWithArray:@[@"apple", @"banana", @"orange"]];
// Mutable sets
NSMutableSet *mutFruitsSet = [NSMutableSet setWithObjects:@"apple", @"banana", @"orange", nil];
[mutFruitsSet addObject:@"grape"];
[mutFruitsSet removeObject:@"apple"];
// Dictionary
NSDictionary *fruitColorsDictionary = @{
@"apple" : @"red",
@"banana" : @"yellow",
@"orange" : @"orange",
@"grape" : @"purple"
// In dictionaryWithObjectsAndKeys you specify the value and then the key:
NSDictionary *fruitColorsDictionary2 = [NSDictionary dictionaryWithObjectsAndKeys:
@"red", @"apple",
@"yellow", @"banana",
@"orange", @"orange",
@"purple", @"grape",
// Mutable dictionary
NSMutableDictionary *mutFruitColorsDictionary = [NSMutableDictionary dictionaryWithDictionary:fruitColorsDictionary];
[mutFruitColorsDictionary setObject:@"green" forKey:@"apple"];
[mutFruitColorsDictionary removeObjectForKey:@"grape"];


Blocks are functions that behaves as objects so they can be passed to functions or stored in arrays or dictionaries. Also, they can represent a value if they are given values so it's similar to lambdas.
returnType (^blockName)(argumentType1, argumentType2, ...) = ^(argumentType1 param1, argumentType2 param2, ...){
//Perform operations here
// For example
int (^suma)(int, int) = ^(int a, int b){
return a+b;
NSLog(@"3+4 = %d", suma(3,4));
It's also possible to define a block type to be used as a parameter in functions:
// Define the block type
typedef void (^callbackLogger)(void);
// Create a bloack with the block type
callbackLogger myLogger = ^{
NSLog(@"%@", @"This is my block");
// Use it inside a function as a param
void genericLogger(callbackLogger blockParam) {
NSLog(@"%@", @"This is my function");
// Call it inline
NSLog(@"%@", @"This is my second block");


// Manager to manage files
NSFileManager *fileManager = [NSFileManager defaultManager];
// Check if file exists:
if ([fileManager fileExistsAtPath:@"/path/to/file.txt" ] == YES) {
NSLog (@"File exists");
// copy files
if ([fileManager copyItemAtPath: @"/path/to/file1.txt" toPath: @"/path/to/file2.txt" error:nil] == YES) {
NSLog (@"Copy successful");
// Check if the content of 2 files match
if ([fileManager contentsEqualAtPath:@"/path/to/file1.txt" andPath:@"/path/to/file2.txt"] == YES) {
NSLog (@"File contents match");
// Delete file
if ([fileManager removeItemAtPath:@"/path/to/file1.txt" error:nil]) {
NSLog(@"Removed successfully");
It's also possible to manage files using NSURL objects instead of NSString objects. The method names are similar, but with URL instead of Path.
NSURL *fileSrc = [NSURL fileURLWithPath:@"/path/to/file1.txt"];
NSURL *fileDst = [NSURL fileURLWithPath:@"/path/to/file2.txt"];
[fileManager moveItemAtURL:fileSrc toURL:fileDst error: nil];
Most basic classes has a method writeToFile:<path> atomically:<YES> encoding:<encoding> error:nil defined that allows them to be directly be written to a file:
NSString* tmp = @"something temporary";
[tmp writeToFile:@"/tmp/tmp1.txt" atomically:YES encoding:NSASCIIStringEncoding error:nil];