Type qualifier and friends

C and objective-C type qualifiers

Transcript

1. Type Qualifiers and Friends Felix Chern (dryman)
2. Felix Chern (dryman) iOS developer github: idryman twitter: @idryman blog: idryman.org
3. Daily used C/Obj-C const int * const ptr; const int * (* const * ptr)(float); int fun(char * restrict src, char * restrict src); UIColor* __autoreleasing red = ...; void (^block)(int volatile *, int volatile *);
4. Daily used C/Obj-C const int * const ptr; const int * (* const * ptr)(float); int fun(char * restrict src, char * restrict src); UIColor* __autoreleasing red = ...; Understand standard C89 declarations void (^block)(int volatile *, int volatile *);
5. Daily used C/Obj-C const int * const ptr; const int * (* const * ptr)(float); int fun(char * restrict src, char * restrict src); UIColor* __autoreleasing red = ...; C99 optimization keywords void (^block)(int volatile *, int volatile *);
6. Daily used C/Obj-C const int * const ptr; const int * (* const * ptr)(float); int fun(char * restrict src, char * restrict src); void (^block)(int volatile *, int volatile *); UIColor* __autoreleasing red = ...; Lockless operations
7. Daily used C/Obj-C const int * const ptr; const int * (* const * ptr)(float); int fun(char * restrict src, char * restrict src); UIColor* __autoreleasing red = ...; Objective-C ARC keywords void (^block)(int volatile *, int volatile *);
8. C declaration
9. C declaration is HARD!!
10. Rule1: read from right to left
11. int const * intPtr;
12. int const * intPtr; Declare variable intPtr
13. int const * intPtr; Declare variable intPtr as a pointer to
14. int const * intPtr; Declare variable intPtr as a pointer to const int
15. int const * intPtr; Declare variable intPtr as a pointer to const int const int a = 4; int const * intPtr = &a; int b = 5; intPtr = &b; //compile error
16. int * const a; // const pointer to int int const * const a; // const pointer to const int int const * a; // pointer to const int const int * a; // pointer to const int If no type/pointer on left, the qualifier applies to type next to it right
17. Rule2: postfix operator () [] precedence is higher
18. int const arr[3]; arr [3] const int Declare arr as array 3 of const int int * const func(float); func (float) const * int Declare func as function(float) returning const pointer to int
19. int const arr[3]; arr [3] const int Declare arr as array 3 of const int int * const func(float); func (float) const * int Declare func as function(float) returning const pointer to int
20. int const arr[3]; arr [3] const int Declare arr as array 3 of const int int * const func(float); func (float) const * int Declare func as function(float) returning const pointer to int
21. int const arr[3]; arr [3] const int Declare arr as array 3 of const int int * const func(float); func (float) const * int Declare func as function(float) returning const pointer to int
22. int const arr[3]; arr [3] const int Declare arr as array 3 of const int int * const func(float); func (float) const * int Declare func as function(float) returning const pointer to int
23. int const arr[3]; arr [3] const int Declare arr as array 3 of const int int * const func(float); func (float) const * int Declare func as function(float) returning const pointer to int
24. int const arr[3]; arr [3] const int Declare arr as array 3 of const int int * const func(float); func (float) const * int Declare func as function(float) returning const pointer to int
25. Rule 3: Surrounding parenthesis has greatest precedence
26. int (*const arr)[3]; arr const * [3] int Declare arr as const pointer to array 3 of int int (* const * func[2])(float); func [2] * const * (float) int func is array 2 of pointer to const pointer to function(float) returning int
27. int (*const arr)[3]; arr const * [3] int Declare arr as const pointer to array 3 of int int (* const * func[2])(float); func [2] * const * (float) int func is array 2 of pointer to const pointer to function(float) returning int
28. int (*const arr)[3]; arr const * [3] int Declare arr as const pointer to array 3 of int int (* const * func[2])(float); func [2] * const * (float) int func is array 2 of pointer to const pointer to function(float) returning int
29. int (*const arr)[3]; arr const * [3] int Declare arr as const pointer to array 3 of int int (* const * func[2])(float); func [2] * const * (float) int func is array 2 of pointer to const pointer to function(float) returning int
30. int (*const arr)[3]; arr const * [3] int Declare arr as const pointer to array 3 of int int (* const * func[2])(float); func [2] * const * (float) int func is array 2 of pointer to const pointer to function(float) returning int
31. int (*const arr)[3]; arr const * [3] int Declare arr as const pointer to array 3 of int int (* const * func[2])(float); func [2] * const * (float) int func is array 2 of pointer to const pointer to function(float) returning int
32. int (*const arr)[3]; arr const * [3] int Declare arr as const pointer to array 3 of int int (* const * func[2])(float); func [2] * const * (float) int func is array 2 of pointer to const pointer to function(float) returning int
33. int (*const arr)[3]; arr const * [3] int Declare arr as const pointer to array 3 of int int (* const * func[2])(float); func [2] * const * (float) int func is array 2 of pointer to const pointer to function(float) returning int
34. int (*const arr)[3]; arr const * [3] int Declare arr as const pointer to array 3 of int int (* const * func[2])(float); func [2] * const * (float) int func is array 2 of pointer to const pointer to function(float) returning int
35. int (*const arr)[3]; arr const * [3] int Declare arr as const pointer to array 3 of int int (* const * func[2])(float); func [2] * const * (float) int func is array 2 of pointer to const pointer to function(float) returning int
36. int (^(^ adder)(int))(int) adder ^(int) ^(int) int adder is a block(int) returning block(int) returning int Now you can read any kind of type declarations!!
37. Type qualifiers
38. • const (C89) • volatile (C89) • restrict (C99) • __weak • __strong • __autoreleasing • __unsafe_unretained
39. Storage specifiers
40. • static (C89) • auto (default, C89) • extern (C89) • register (not a type qualifier, C89) • __block (Clang extension) • typedef (act like storage specifier)
41. static const int a; storage specifier type qualifier typedef const int MyInt typedef static int MyInt
42. Objective-C ARC qualifiers • Used for explicit ARC declaration • Apply on objective-c pointers
43. __weak FCController * w_self = self; FCController __weak * w_self = self; FCController * __weak w_self = self;
44. FCController * __weak w_self = self; self.block = ^{ FCController * __strong s_self = w_self; if (s_self != nil) { // self retained s_self.point = CGMakePoint(....); // blah } }; Use weak self to break retain cycle
45. CGColorRef redRef; @autorelease{ UIColor* __autoreleasing red = [UIColor redColor]; redRef = CFRetain([red CGColor]); // redRef retain count: 2 } // redRef retain count: 1 CALayer *layer = [CALayer layer]; [layer setBackgroundColor redRef]; CFRelease(redRef); // redRef retain count: 0, freed Explicitly call autorelease
46. void function (void* data) { int [] array; array = (int []) data; // fail } int [] is implicit int * const void function (void* data) { int * array; array = (int *) data; }
47. See also • http://www.idryman.org/blog/2012/10/29/type-qualifiers/ • http://www.vineetgupta.com/2011/03/deciphering-complex-c-declarations/ • http://cdecl.org volatile, restrict
48. Questions?