Type qualifier and friends

C and objective-C type qualifiers

Transcript

1. Type Qualifiers and
   Friends
   Felix Chern (dryman)
   

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2. Felix Chern
   (dryman)
   iOS developer
   github: idryman
   twitter: @idryman
   blog: idryman.org
   

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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 *);
   

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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 *);
   

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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 *);
   

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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
   

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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 *);
   

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8. C declaration
   

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9. C declaration
   is HARD!!
   

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10. Rule1:
    read from right to left
    

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11. int const * intPtr;
    

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12. int const * intPtr;
    Declare variable intPtr
    

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13. int const * intPtr;
    Declare variable intPtr as a pointer to
    

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14. int const * intPtr;
    Declare variable intPtr as a pointer to const int
    

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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
    

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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
    

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17. Rule2:
    postfix operator () []
    precedence is higher
    

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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
    

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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
    

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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
    

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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
    

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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
    

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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
    

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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
    

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25. Rule 3:
    Surrounding
    parenthesis has greatest
    precedence
    

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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
    

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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
    

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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
    

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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
    

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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
    

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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
    

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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
    

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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
    

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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
    

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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
    

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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!!
    

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37. Type qualifiers
    

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38. • const (C89)
    • volatile (C89)
    • restrict (C99)
    • __weak
    • __strong
    • __autoreleasing
    • __unsafe_unretained
    

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39. Storage specifiers
    

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40. • static (C89)
    • auto (default, C89)
    • extern (C89)
    • register (not a type qualifier, C89)
    • __block (Clang extension)
    • typedef (act like storage specifier)
    

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41. static const int a;
    storage specifier type qualifier
    typedef const int MyInt
    typedef static int MyInt
    

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42. Objective-C
    ARC qualifiers
    • Used for explicit ARC declaration
    • Apply on objective-c pointers
    

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43. __weak FCController * w_self = self;
    FCController __weak * w_self = self;
    FCController * __weak w_self = self;
    

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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
    

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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
    

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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;
    }
    

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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
    

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48. Questions?
    

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