Git附件与GitHub？(Git Annex with GitHub?)

 让我们说返回的数组大小为8，它在内存中看起来像这样： 
 
+---+
| c |
+---+
  |
  v
  +---+---+---+---+---+---+---+---+
  | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
  +---+---+---+---+---+---+---+---+
 
 （里面的数字是索引。） 
 
 现在，如果你创建一个新的变量e指向c + size ，它将指向一个超出数据末尾的变量： 
 
+---+                           +---+
| c |                           | e |
+---+                           +---+
  |                               |
  v                               v
  +---+---+---+---+---+---+---+---+
  | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
  +---+---+---+---+---+---+---+---+
 
 如果你从e减去1它现在指向索引7 ： 
 
+---+                       +---+
| c |                       | e |
+---+                       +---+
  |                           |
  v                           v
  +---+---+---+---+---+---+---+---+
  | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
  +---+---+---+---+---+---+---+---+
 
 如果你减去两个（总共） e将指向索引6 ，减去3并且e将指向索引5并且减去4并且指向的索引将是4 。 如果你减去5 ，指针e将指向索引3 ： 
 
+---+       +---+
| c |       | e |
+---+       +---+
  |           |
  v           v
  +---+---+---+---+---+---+---+---+
  | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
  +---+---+---+---+---+---+---+---+
 
 而且距离结尾不是四个字节，距离结尾的五个字节。 
 
 所以你应该这样做 
 
char* end = c + size - 4;  /* Subtract by 4 and not 5 */
 
 
 如果数据来自其他系统，例如通过Internet，您还应该注意字节顺序 。 

Lets say the returned array is of size 8, it would look something like this in memory:
 
+---+
| c |
+---+
  |
  v
  +---+---+---+---+---+---+---+---+
  | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
  +---+---+---+---+---+---+---+---+
 
(The numbers inside is the indexes.)
 
Now if you make a new variable e to point at c + size it will point point to one beyond the end of the data:
 
+---+                           +---+
| c |                           | e |
+---+                           +---+
  |                               |
  v                               v
  +---+---+---+---+---+---+---+---+
  | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
  +---+---+---+---+---+---+---+---+
 
If you subtract 1 from e it now points to index 7:
 
+---+                       +---+
| c |                       | e |
+---+                       +---+
  |                           |
  v                           v
  +---+---+---+---+---+---+---+---+
  | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
  +---+---+---+---+---+---+---+---+
 
If you subtract two (in total) e would point to index 6, subtract 3 and e would be pointing at index 5 and subtract 4 and the index pointed to would be 4. If you subtract 5 the pointer e would point to index 3:
 
+---+       +---+
| c |       | e |
+---+       +---+
  |           |
  v           v
  +---+---+---+---+---+---+---+---+
  | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
  +---+---+---+---+---+---+---+---+
 
And that's not four bytes from the end, that's five bytes from the end.
 
So you should be doing e.g.
 
char* end = c + size - 4;  /* Subtract by 4 and not 5 */
 
 
You should also be careful of the endianness, if the data comes from other systems e.g. over the Internet.