https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/ObjCRuntimeGuide/Articles/ocrtTypeEncodings.html
| Code | Meaning |
| c | A char |
| i | An int |
| s | A short |
| l | A long，l is treated as a 32-bit quantity on 64-bit programs. |
| q | A long long |
| C | An unsigned char |
| I | An unsigned int |
| S | An unsigned short |
| L | An unsigned long |
| Q | An unsigned long long |
| f | A float |
| d | A double |
| B | A C++ bool or a C99 _Bool |
| v | A void |
| * | A character string (char *) |
| @ | An object (whether statically typed or typed id) |
| # | A class object (Class) |
| : | A method selector (SEL) |
| [array type] | An array |
| {name=type...} | A structure |
| (name=type...) | A union |
| bnum | A bit field of num bits |
| ^type | A pointer to type |
| ? | An unknown type (among other things, this code is used for function pointers) |
| r | const |
| n | in |
| N | inout |
| O | out |
| O | bycopy |
| R | byref |
| V | oneway |