Objective-C Reference

#import <Foundation/Foundation.h>

int main() {
    @autoreleasepool {
        // NSLog adds a timestamp and newline
        NSLog(@"Hello, World!");
    }
    return 0;
}

# Compile and run
clang -framework Foundation main.m -o main
./main

// Single-line comment

/* Multi-line
   comment */

#import <Foundation/Foundation.h> // Smart include (prevents recursion)
#import "LocalHeader.h"

#import <Foundation/Foundation.h>

// Standard C exit
exit(1);

@try {
    @throw [NSException exceptionWithName:@"Fail" reason:@"Err" userInfo:nil];
} @catch (NSException *e) {
    NSLog(@"Caught: %@", e.reason);
} @finally {
    NSLog(@"Cleanup");
}

NSString *name = @"ObjC"; // Object pointer
NSInteger count = 10;      // Primitive (typedef to long or int)
BOOL active = YES;         // Boolean (YES/NO)

NSInteger i = 100;   // Signed (platform width)
NSUInteger u = 200;  // Unsigned
int32_t i32 = 1000;  // Fixed width (C99)

NSString *s = @"123";
NSInteger i = [s integerValue];
NSString *back = [NSString stringWithFormat:@"%ld", (long)i];

id obj = nil;
if (!obj) { NSLog(@"Object is nil"); }

int x = 1;
if (x) { NSLog(@"True"); }

NSDictionary *env = [[NSProcessInfo processInfo] environment];
NSString *path = env[@"PATH"];

NSDate *now = [NSDate date];
NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
[fmt setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
NSLog(@"%@", [fmt stringFromDate:now]);

float a = 10 / 3.0;
BOOL b = YES && NO;
NSInteger c = 1 << 4; // 16

NSString *text = @"price: 100";
NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:@"\\d+" options:0 error:nil];
NSTextCheckingResult *match = [regex firstMatchInString:text options:0 range:NSMakeRange(0, text.length)];
if (match) {
    NSLog(@"%@", [text substringWithRange:match.range]);
}

NSArray *args = [[NSProcessInfo processInfo] arguments];
if (args.count > 1) {
    NSLog(@"First arg: %@", args[1]);
}

// Method declaration (in @interface)
- (NSInteger)add:(NSInteger)a to:(NSInteger)b {
    return a + b;
}

// C-style function
int multiply(int a, int b) { return a * b; }

__strong NSString *s1 = @"Stay";
__weak NSString *s2 = s1; // Doesn't retain
__unsafe_unretained NSString *s3 = s1; // Dangling pointer potential

// POSIX memory
void *ptr = malloc(1024);
free(ptr);

for (int i = 0; i < 3; i++) { NSLog(@"%d", i); }

int x = 0;
while (x < 2) { x++; }

for (int i = 0; i < 5; i++) {
    if (i == 1) continue;
    if (i == 3) break;
    NSLog(@"%d", i);
}

NSArray *arr = @[@"a", @"b"];
for (NSString *s in arr) {
    NSLog(@"%@", s);
}

[arr enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
    NSLog(@"%lu: %@", (unsigned long)idx, obj);
}];

NSString *s = @"  hello  ";
NSString *trimmed = [s stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];
NSString *joined = [@[@"a", @"b"] componentsJoinedByString:@"-"];

NSString *path = [@"/tmp" stringByAppendingPathComponent:@"test.txt"];

NSFileHandle *handle = [NSFileHandle fileHandleForReadingAtPath:@"data.bin"];
NSData *chunk = [handle readDataOfLength:4096];
[handle closeFile];

NSString *content = [NSString stringWithContentsOfFile:@"file.txt" encoding:NSUTF8StringEncoding error:nil];
NSData *data = [NSData dataWithContentsOfFile:@"file.txt"];

NSMutableData *data = [NSMutableData dataWithCapacity:12];
int32_t val = 42;
[data appendBytes:&val length:sizeof(val)];

int a = 0b1010 & 0b1100; // 8
int b = 0b1010 | 0b1100; // 14
int c = ~0b0001;

NSString *hex = [NSString stringWithFormat:@"%x", 255]; // "ff"
unsigned int val;
NSScanner *scanner = [NSScanner scannerWithString:@"ff"];
[scanner scanHexInt:&val]; // val = 255

NSArray *arr = @[@1, @2];               // Immutable Array
NSMutableArray *mArr = [arr mutableCopy]; // Mutable
NSDictionary *dict = @{@"key": @"val"}; // Literal Dictionary
NSSet *set = [NSSet setWithArray:@[@1, @1, @2]];

NSData *data = [@"{\"id\": 42}" dataUsingEncoding:NSUTF8StringEncoding];
NSDictionary *json = [NSJSONSerialization JSONObjectWithData:data options:0 error:nil];
NSLog(@"%@", json[@"id"]);

// Using NSStream for Foundation-level TCP
NSInputStream *input;
NSOutputStream *output;
[NSStream getStreamsToHostWithName:@"localhost" port:8080 inputStream:&input outputStream:&output];
[input open]; [output open];

#import <sys/socket.h>
#import <netinet/in.h>

int sock = socket(AF_INET, SOCK_DGRAM, 0);
// Standard POSIX socket usage...
close(sock);

// Grand Central Dispatch (GCD)
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    NSLog(@"In background");
});

// NSOperationQueue
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
    NSLog(@"On main thread");
}];

#import <sqlite3.h>

sqlite3 *db;
sqlite3_open(":memory:", &db);
sqlite3_exec(db, "CREATE TABLE t(id INT)", NULL, NULL, NULL);
sqlite3_close(db);