Type Encodings-runtime

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)

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出处:
https://developer.apple.com/library/content/documentation/Cocoa/Conceptual/ObjCRuntimeGuide/Articles/ocrtTypeEncodings.html