Type Encodings

Type Encodings：

NSLog(@"int : %s", @encode(int));
NSLog(@"float: %s", @encode(float));
NSLog(@"float *: %s", @encode(float*));
NSLog(@"char: %s", @encode(char));
NSLog(@"char *: %s", @encode(char *));
NSLog(@"BOOL: %s", @encode(BOOL));
NSLog(@"void: %s", @encode(void));
NSLog(@"void *: %s", @encode(void *));

NSLog(@"NSObject * : %s", @encode(NSObject *));
NSLog(@"NSObject : %s", @encode(NSObject));
NSLog(@"[NSObject] : %s", @encode(typeof([NSObject class])));
NSLog(@"NSError ** : %s", @encode(typeof(NSError **)));

int intArray[5] = {1, 2, 3, 4, 5};
NSLog(@"int[] : %s", @encode(typeof(intArray))); !

float floatArray[3] = {0.1f, 0.2f, 0.3f};
NSLog(@"float[] : %s", @encode(typeof(floatArray))); !

typedef struct _struct
{
    short a;
    long long b;
    unsigned long long c;
} Struct;

NSLog(@"struct     : %s", @encode(typeof(Struct)));

int :i
float :f
float * :^f
char :c
char * :*
BOOL :c
void :v
void * :^v

NSObject * : @
NSObject : #
[NSObject] : {NSObject=#}
NSError ** : ^@
int[]: [5i]
float[]: [3f]
struct: {_struct=sqQ}

There are some interesting takeaways from this:

1. Whereas the standard encoding for pointers is a preceding ^, char gets its own code: . This makes sense conceptually, since C strings are thought to be entities in and of themselves, rather than a pointer to something else.

2. BOOL is c, rather than i, as one might expect. Reason being, char is smaller than an int, and when Objective-C was originally designed in the 80's, bits (much like the US Dollar) were more valuable than they are today.

3. Passing NSObject directly yields #. However, passing [NSObject class] yields a struct named NSObject with a single class field. That is, of course, the isa field, which all NSObject instances have to signify their type.

Method Encodings

As mentioned in Apple's "Objective-C Runtime Programming Guide", there are a handful of type encodings that are used internally, but cannot be returned with @encode.

These are the type qualifiers for methods declared in a protocol: