1.截獲自動(dòng)變量

int value = 1;
    void (^blk)(void) = ^{
        printf("Block function :%d",value);
      };
    value = 2;
    blk();

將上面代碼進(jìn)行clang轉(zhuǎn)換

struct __main_block_impl_0 {
  struct __block_impl impl;
  struct __main_block_desc_0* Desc;
  int value;
  __main_block_impl_0(void *fp, struct __main_block_desc_0 *desc, int _value, int flags=0) : value(_value) {
    impl.isa = &_NSConcreteStackBlock;
    impl.Flags = flags;
    impl.FuncPtr = fp;
    Desc = desc;
  }
};
static void __main_block_func_0(struct __main_block_impl_0 *__cself) {
  int value = __cself->value; // bound by copy

        printf("Block function :%d",value);
      }

static struct __main_block_desc_0 {
  size_t reserved;
  size_t Block_size;
} __main_block_desc_0_DATA = { 0, sizeof(struct __main_block_impl_0)};
int main(int argc, char * argv[]) {

    int value = 1;
    void (*blk)(void) = ((void (*)())&__main_block_impl_0((void *)__main_block_func_0, &__main_block_desc_0_DATA, value));
    value = 2;
    ((void (*)(__block_impl *))((__block_impl *)blk)->FuncPtr)((__block_impl *)blk);

    return 0;

}

我們可以看到 value 被捕獲到__main_block_impl_0結(jié)構(gòu)體中了

2.__block 說明符

我們先看一下 靜態(tài)全局變量 全局變量 和靜態(tài)變量在clang中的表示

int globalValue = 0;
static int staticGlobalValue = 1;

struct __main_block_impl_0 {
  struct __block_impl impl;
  struct __main_block_desc_0* Desc;
  int *staticValue;
  __main_block_impl_0(void *fp, struct __main_block_desc_0 *desc, int *_staticValue, int flags=0) : staticValue(_staticValue) {
    impl.isa = &_NSConcreteStackBlock;
    impl.Flags = flags;
    impl.FuncPtr = fp;
    Desc = desc;
  }
};
static void __main_block_func_0(struct __main_block_impl_0 *__cself) {
  int *staticValue = __cself->staticValue; // bound by copy

        globalValue += 1;
        staticGlobalValue += 1;
        (*staticValue) += 1;
        printf("Block function :%d",(*staticValue));
      }

static struct __main_block_desc_0 {
  size_t reserved;
  size_t Block_size;
} __main_block_desc_0_DATA = { 0, sizeof(struct __main_block_impl_0)};
int main(int argc, char * argv[]) {

    static int staticValue = 2;
    void (*blk)(void) = ((void (*)())&__main_block_impl_0((void *)__main_block_func_0, &__main_block_desc_0_DATA, &staticValue));
    ((void (*)(__block_impl *))((__block_impl *)blk)->FuncPtr)((__block_impl *)blk);

    return 0;

}

我們看到只有靜態(tài)變量進(jìn)行了轉(zhuǎn)換免胃，全局和動(dòng)態(tài)變量都和之前完全相同寄症，我們?cè)賮砜窗鸯o態(tài)變量轉(zhuǎn)成__block

struct __main_block_impl_0 {
  struct __block_impl impl;
  struct __main_block_desc_0* Desc;
  __Block_byref_staticValue_0 *staticValue; // by ref
  __main_block_impl_0(void *fp, struct __main_block_desc_0 *desc, __Block_byref_staticValue_0 *_staticValue, int flags=0) : staticValue(_staticValue->__forwarding) {
    impl.isa = &_NSConcreteStackBlock;
    impl.Flags = flags;
    impl.FuncPtr = fp;
    Desc = desc;
  }
};
static void __main_block_func_0(struct __main_block_impl_0 *__cself) {
  __Block_byref_staticValue_0 *staticValue = __cself->staticValue; // bound by ref

        globalValue += 1;
        staticGlobalValue += 1;
        (staticValue->__forwarding->staticValue) += 1;
        printf("Block function :%d",(staticValue->__forwarding->staticValue));
      }
static void __main_block_copy_0(struct __main_block_impl_0*dst, struct __main_block_impl_0*src) {_Block_object_assign((void*)&dst->staticValue, (void*)src->staticValue, 8/*BLOCK_FIELD_IS_BYREF*/);}

static void __main_block_dispose_0(struct __main_block_impl_0*src) {_Block_object_dispose((void*)src->staticValue, 8/*BLOCK_FIELD_IS_BYREF*/);}

static struct __main_block_desc_0 {
  size_t reserved;
  size_t Block_size;
  void (*copy)(struct __main_block_impl_0*, struct __main_block_impl_0*);
  void (*dispose)(struct __main_block_impl_0*);
} __main_block_desc_0_DATA = { 0, sizeof(struct __main_block_impl_0), __main_block_copy_0, __main_block_dispose_0};
int main(int argc, char * argv[]) {

   __attribute__((__blocks__(byref))) __Block_byref_staticValue_0 staticValue = {(void*)0,(__Block_byref_staticValue_0 *)&staticValue, 0, sizeof(__Block_byref_staticValue_0), 2};
    void (*blk)(void) = ((void (*)())&__main_block_impl_0((void *)__main_block_func_0, &__main_block_desc_0_DATA, (__Block_byref_staticValue_0 *)&staticValue, 570425344));
    ((void (*)(__block_impl *))((__block_impl *)blk)->FuncPtr)((__block_impl *)blk);

    return 0;

}

此時(shí)__block 竟然變成__Block_byref_staticValue_0結(jié)構(gòu)體，給staticValue靜態(tài)變量賦值的時(shí)候，使用了指向該靜態(tài)變量的指針弄跌，而向__block變量賦值的時(shí)候__Block_byref_staticValue_0 結(jié)構(gòu)體的成員變量__forwarding 持有該實(shí)例自身的指針

static void __main_block_func_0(struct __main_block_impl_0 *__cself) {
  __Block_byref_staticValue_0 *staticValue = __cself->staticValue; // bound by ref

        globalValue += 1;
        staticGlobalValue += 1;
        (staticValue->__forwarding->staticValue) += 1;
        printf("Block function :%d",(staticValue->__forwarding->staticValue));
      }