c 双字段访问，为什么会有 struct->field_1->field_2

Question

这是一个简单的问题，它可能是重复的，但我能找到它，

有人可以解释一下这一行发生了什么

  BlockPrefix_t *makeFreeBlock(void *addr, size_t size) { 
  BlockPrefix_t *p = addr;
  void *limitAddr = addr + size;
  BlockSuffix_t *s = limitAddr - align8(sizeof(BlockSuffix_t));
  p->suffix = s;
  s->prefix = p;
  p->allocated = 0;
  return p;
}

这是代码:

BlockSuffix_t *newBlock = (void *)r->suffix + requiredSize;
newBlock->prefix = r;
BlockPrefix_t *temp = (void *)newBlock + suffixSize;
temp->suffix = (void *)nextRegion->suffix;
temp->suffix->prefix = temp;

我不明白为什么要双重访问？

Answer 1

你必须这样读这一行:

(temp->suffix)->prefix = temp.

您正在将“temp->suffix”指向的数据结构的字段“prefix”的值分配给temp本身。