Question

我目前正在研究mergesort算法。我有三个功能。 list_sort_merge，mergelist和splitlist。 list_sort_merge调用另外两个来拆分并合并列表。我无法正常工作。那么当我运行GDB时会发生的事情是我通过split函数并自己获取每个数字，如下例所示：

427
42.7
4.2.7

然后，mergesort出现了并且我发生了段错误。会发生什么是right_list和left_list没有传递给mergesort。当mergesort在函数comp_proc中进行比较时，它表示它们都是NULL。

我认为问题来自分裂功能。

谁能看到我在这里做错了什么？

Answer 1

以下是解释： http://www.chiark.greenend.org.uk/~sgtatham/algorithms/listsort.html

和示例代码： http://www.chiark.greenend.org.uk/~sgtatham/algorithms/listsort.c

Answer 2

我最终重新实现了列表函数以适合自己，因为我无法弄清楚代码中某些函数的接口是如何工作的，即使在注释中提示之后也是如此。新代码仍在使用双向链接列表，但我将list_node_t重命名为node_t并将current_list_size缩短为size。有一个功能可以插入尾部，另一个可以从头部移除;其他功能相当直接。

现在有三个文件：主合并排序源代码（mergelist.c），包括测试main()程序和问题中三个函数的修订版本;列表标题（list.h）定义list_t类型的接口;以及实现list.c类型的列表源代码（list_t）。

兴奋主要在主要代码中，但其余部分对于让事情发挥作用是必要的。排序按降序排序（最大值优先）。 mergelist.c的代码中突出显示了关键的更改（我记得，而不是列表函数的接口）。关键调试工具是dump_list()函数。类似的东西是 sine qua non ，用于调试排序和列表等。

严格地说，以_t结尾的类型名称是为实现保留的（参见What does a type followed by _t (underscore t) represent?）。

示例输出

在Mac OS X 10.8.5上使用GCC 4.8.1编译，64位指针。

List Before (0x7FEC21C039A0)
Head 0x7FEC21C039C0, Tail 0x7FEC21C03AE0, Size 10
 1: Node 0x7FEC21C039C0, Next 0x7FEC21C039E0, Prev 0x000000000000, Data 1
 2: Node 0x7FEC21C039E0, Next 0x7FEC21C03A00, Prev 0x7FEC21C039C0, Data 3
 3: Node 0x7FEC21C03A00, Next 0x7FEC21C03A20, Prev 0x7FEC21C039E0, Data 9
 4: Node 0x7FEC21C03A20, Next 0x7FEC21C03A40, Prev 0x7FEC21C03A00, Data 2
 5: Node 0x7FEC21C03A40, Next 0x7FEC21C03A60, Prev 0x7FEC21C03A20, Data 7
 6: Node 0x7FEC21C03A60, Next 0x7FEC21C03A80, Prev 0x7FEC21C03A40, Data 5
 7: Node 0x7FEC21C03A80, Next 0x7FEC21C03AA0, Prev 0x7FEC21C03A60, Data 8
 8: Node 0x7FEC21C03AA0, Next 0x7FEC21C03AC0, Prev 0x7FEC21C03A80, Data 6
 9: Node 0x7FEC21C03AC0, Next 0x7FEC21C03AE0, Prev 0x7FEC21C03AA0, Data 0
10: Node 0x7FEC21C03AE0, Next 0x000000000000, Prev 0x7FEC21C03AC0, Data 4
List -->>list_sort_merge() (0x7FEC21C039A0)
Head 0x7FEC21C039C0, Tail 0x7FEC21C03AE0, Size 10
 1: Node 0x7FEC21C039C0, Next 0x7FEC21C039E0, Prev 0x000000000000, Data 1
 2: Node 0x7FEC21C039E0, Next 0x7FEC21C03A00, Prev 0x7FEC21C039C0, Data 3
 3: Node 0x7FEC21C03A00, Next 0x7FEC21C03A20, Prev 0x7FEC21C039E0, Data 9
 4: Node 0x7FEC21C03A20, Next 0x7FEC21C03A40, Prev 0x7FEC21C03A00, Data 2
 5: Node 0x7FEC21C03A40, Next 0x7FEC21C03A60, Prev 0x7FEC21C03A20, Data 7
 6: Node 0x7FEC21C03A60, Next 0x7FEC21C03A80, Prev 0x7FEC21C03A40, Data 5
 7: Node 0x7FEC21C03A80, Next 0x7FEC21C03AA0, Prev 0x7FEC21C03A60, Data 8
 8: Node 0x7FEC21C03AA0, Next 0x7FEC21C03AC0, Prev 0x7FEC21C03A80, Data 6
 9: Node 0x7FEC21C03AC0, Next 0x7FEC21C03AE0, Prev 0x7FEC21C03AA0, Data 0
10: Node 0x7FEC21C03AE0, Next 0x000000000000, Prev 0x7FEC21C03AC0, Data 4
List Split-L (0x7FEC21C03B20)
Head 0x7FEC21C039C0, Tail 0x7FEC21C03A40, Size 5
 1: Node 0x7FEC21C039C0, Next 0x7FEC21C039E0, Prev 0x000000000000, Data 1
 2: Node 0x7FEC21C039E0, Next 0x7FEC21C03A00, Prev 0x7FEC21C039C0, Data 3
 3: Node 0x7FEC21C03A00, Next 0x7FEC21C03A20, Prev 0x7FEC21C039E0, Data 9
 4: Node 0x7FEC21C03A20, Next 0x7FEC21C03A40, Prev 0x7FEC21C03A00, Data 2
 5: Node 0x7FEC21C03A40, Next 0x000000000000, Prev 0x7FEC21C03A20, Data 7
List Split-R (0x7FEC21C03B00)
Head 0x7FEC21C03A60, Tail 0x7FEC21C03AE0, Size 5
 1: Node 0x7FEC21C03A60, Next 0x7FEC21C03A80, Prev 0x000000000000, Data 5
 2: Node 0x7FEC21C03A80, Next 0x7FEC21C03AA0, Prev 0x7FEC21C03A60, Data 8
 3: Node 0x7FEC21C03AA0, Next 0x7FEC21C03AC0, Prev 0x7FEC21C03A80, Data 6
 4: Node 0x7FEC21C03AC0, Next 0x7FEC21C03AE0, Prev 0x7FEC21C03AA0, Data 0
 5: Node 0x7FEC21C03AE0, Next 0x000000000000, Prev 0x7FEC21C03AC0, Data 4
List -->>list_sort_merge() (0x7FEC21C03B20)
Head 0x7FEC21C039C0, Tail 0x7FEC21C03A40, Size 5
 1: Node 0x7FEC21C039C0, Next 0x7FEC21C039E0, Prev 0x000000000000, Data 1
 2: Node 0x7FEC21C039E0, Next 0x7FEC21C03A00, Prev 0x7FEC21C039C0, Data 3
 3: Node 0x7FEC21C03A00, Next 0x7FEC21C03A20, Prev 0x7FEC21C039E0, Data 9
 4: Node 0x7FEC21C03A20, Next 0x7FEC21C03A40, Prev 0x7FEC21C03A00, Data 2
 5: Node 0x7FEC21C03A40, Next 0x000000000000, Prev 0x7FEC21C03A20, Data 7
List Split-L (0x7FEC21C03B60)
Head 0x7FEC21C039C0, Tail 0x7FEC21C03A00, Size 3
 1: Node 0x7FEC21C039C0, Next 0x7FEC21C039E0, Prev 0x000000000000, Data 1
 2: Node 0x7FEC21C039E0, Next 0x7FEC21C03A00, Prev 0x7FEC21C039C0, Data 3
 3: Node 0x7FEC21C03A00, Next 0x000000000000, Prev 0x7FEC21C039E0, Data 9
List Split-R (0x7FEC21C03B40)
Head 0x7FEC21C03A20, Tail 0x7FEC21C03A40, Size 2
 1: Node 0x7FEC21C03A20, Next 0x7FEC21C03A40, Prev 0x000000000000, Data 2
 2: Node 0x7FEC21C03A40, Next 0x000000000000, Prev 0x7FEC21C03A20, Data 7
List -->>list_sort_merge() (0x7FEC21C03B60)
Head 0x7FEC21C039C0, Tail 0x7FEC21C03A00, Size 3
 1: Node 0x7FEC21C039C0, Next 0x7FEC21C039E0, Prev 0x000000000000, Data 1
 2: Node 0x7FEC21C039E0, Next 0x7FEC21C03A00, Prev 0x7FEC21C039C0, Data 3
 3: Node 0x7FEC21C03A00, Next 0x000000000000, Prev 0x7FEC21C039E0, Data 9
List Split-L (0x7FEC21C03BA0)
Head 0x7FEC21C039C0, Tail 0x7FEC21C039E0, Size 2
 1: Node 0x7FEC21C039C0, Next 0x7FEC21C039E0, Prev 0x000000000000, Data 1
 2: Node 0x7FEC21C039E0, Next 0x000000000000, Prev 0x7FEC21C039C0, Data 3
List Split-R (0x7FEC21C03B80)
Head 0x7FEC21C03A00, Tail 0x7FEC21C03A00, Size 1
 1: Node 0x7FEC21C03A00, Next 0x000000000000, Prev 0x000000000000, Data 9
List -->>list_sort_merge() (0x7FEC21C03BA0)
Head 0x7FEC21C039C0, Tail 0x7FEC21C039E0, Size 2
 1: Node 0x7FEC21C039C0, Next 0x7FEC21C039E0, Prev 0x000000000000, Data 1
 2: Node 0x7FEC21C039E0, Next 0x000000000000, Prev 0x7FEC21C039C0, Data 3
List Split-L (0x7FEC21C03BE0)
Head 0x7FEC21C039C0, Tail 0x7FEC21C039C0, Size 1
 1: Node 0x7FEC21C039C0, Next 0x000000000000, Prev 0x000000000000, Data 1
List Split-R (0x7FEC21C03BC0)
Head 0x7FEC21C039E0, Tail 0x7FEC21C039E0, Size 1
 1: Node 0x7FEC21C039E0, Next 0x000000000000, Prev 0x000000000000, Data 3
-->>list_sort_merge()
List List-L (0x7FEC21C03BE0)
Head 0x7FEC21C039C0, Tail 0x7FEC21C039C0, Size 1
 1: Node 0x7FEC21C039C0, Next 0x000000000000, Prev 0x000000000000, Data 1
List List-R (0x7FEC21C03BC0)
Head 0x7FEC21C039E0, Tail 0x7FEC21C039E0, Size 1
 1: Node 0x7FEC21C039E0, Next 0x000000000000, Prev 0x000000000000, Data 3
<<--list_sort_merge()
List <<--list_sort_merge() (0x7FEC21C03BA0)
Head 0x7FEC21C039E0, Tail 0x7FEC21C039C0, Size 2
 1: Node 0x7FEC21C039E0, Next 0x7FEC21C039C0, Prev 0x000000000000, Data 3
 2: Node 0x7FEC21C039C0, Next 0x000000000000, Prev 0x7FEC21C039E0, Data 1
-->>list_sort_merge()
List List-L (0x7FEC21C03BA0)
Head 0x7FEC21C039E0, Tail 0x7FEC21C039C0, Size 2
 1: Node 0x7FEC21C039E0, Next 0x7FEC21C039C0, Prev 0x000000000000, Data 3
 2: Node 0x7FEC21C039C0, Next 0x000000000000, Prev 0x7FEC21C039E0, Data 1
List List-R (0x7FEC21C03B80)
Head 0x7FEC21C03A00, Tail 0x7FEC21C03A00, Size 1
 1: Node 0x7FEC21C03A00, Next 0x000000000000, Prev 0x000000000000, Data 9
<<--list_sort_merge()
List <<--list_sort_merge() (0x7FEC21C03B60)
Head 0x7FEC21C03A00, Tail 0x7FEC21C039C0, Size 3
 1: Node 0x7FEC21C03A00, Next 0x7FEC21C039E0, Prev 0x000000000000, Data 9
 2: Node 0x7FEC21C039E0, Next 0x7FEC21C039C0, Prev 0x7FEC21C03A00, Data 3
 3: Node 0x7FEC21C039C0, Next 0x000000000000, Prev 0x7FEC21C039E0, Data 1
List -->>list_sort_merge() (0x7FEC21C03B40)
Head 0x7FEC21C03A20, Tail 0x7FEC21C03A40, Size 2
 1: Node 0x7FEC21C03A20, Next 0x7FEC21C03A40, Prev 0x000000000000, Data 2
 2: Node 0x7FEC21C03A40, Next 0x000000000000, Prev 0x7FEC21C03A20, Data 7
List Split-L (0x7FEC21C03B80)
Head 0x7FEC21C03A20, Tail 0x7FEC21C03A20, Size 1
 1: Node 0x7FEC21C03A20, Next 0x000000000000, Prev 0x000000000000, Data 2
List Split-R (0x7FEC21C03BA0)
Head 0x7FEC21C03A40, Tail 0x7FEC21C03A40, Size 1
 1: Node 0x7FEC21C03A40, Next 0x000000000000, Prev 0x000000000000, Data 7
-->>list_sort_merge()
List List-L (0x7FEC21C03B80)
Head 0x7FEC21C03A20, Tail 0x7FEC21C03A20, Size 1
 1: Node 0x7FEC21C03A20, Next 0x000000000000, Prev 0x000000000000, Data 2
List List-R (0x7FEC21C03BA0)
Head 0x7FEC21C03A40, Tail 0x7FEC21C03A40, Size 1
 1: Node 0x7FEC21C03A40, Next 0x000000000000, Prev 0x000000000000, Data 7
<<--list_sort_merge()
List <<--list_sort_merge() (0x7FEC21C03B40)
Head 0x7FEC21C03A40, Tail 0x7FEC21C03A20, Size 2
 1: Node 0x7FEC21C03A40, Next 0x7FEC21C03A20, Prev 0x000000000000, Data 7
 2: Node 0x7FEC21C03A20, Next 0x000000000000, Prev 0x7FEC21C03A40, Data 2
-->>list_sort_merge()
List List-L (0x7FEC21C03B60)
Head 0x7FEC21C03A00, Tail 0x7FEC21C039C0, Size 3
 1: Node 0x7FEC21C03A00, Next 0x7FEC21C039E0, Prev 0x000000000000, Data 9
 2: Node 0x7FEC21C039E0, Next 0x7FEC21C039C0, Prev 0x7FEC21C03A00, Data 3
 3: Node 0x7FEC21C039C0, Next 0x000000000000, Prev 0x7FEC21C039E0, Data 1
List List-R (0x7FEC21C03B40)
Head 0x7FEC21C03A40, Tail 0x7FEC21C03A20, Size 2
 1: Node 0x7FEC21C03A40, Next 0x7FEC21C03A20, Prev 0x000000000000, Data 7
 2: Node 0x7FEC21C03A20, Next 0x000000000000, Prev 0x7FEC21C03A40, Data 2
<<--list_sort_merge()
List <<--list_sort_merge() (0x7FEC21C03B20)
Head 0x7FEC21C03A00, Tail 0x7FEC21C039C0, Size 5
 1: Node 0x7FEC21C03A00, Next 0x7FEC21C03A40, Prev 0x000000000000, Data 9
 2: Node 0x7FEC21C03A40, Next 0x7FEC21C039E0, Prev 0x7FEC21C03A00, Data 7
 3: Node 0x7FEC21C039E0, Next 0x7FEC21C03A20, Prev 0x7FEC21C03A40, Data 3
 4: Node 0x7FEC21C03A20, Next 0x7FEC21C039C0, Prev 0x7FEC21C039E0, Data 2
 5: Node 0x7FEC21C039C0, Next 0x000000000000, Prev 0x7FEC21C03A20, Data 1
List -->>list_sort_merge() (0x7FEC21C03B00)
Head 0x7FEC21C03A60, Tail 0x7FEC21C03AE0, Size 5
 1: Node 0x7FEC21C03A60, Next 0x7FEC21C03A80, Prev 0x000000000000, Data 5
 2: Node 0x7FEC21C03A80, Next 0x7FEC21C03AA0, Prev 0x7FEC21C03A60, Data 8
 3: Node 0x7FEC21C03AA0, Next 0x7FEC21C03AC0, Prev 0x7FEC21C03A80, Data 6
 4: Node 0x7FEC21C03AC0, Next 0x7FEC21C03AE0, Prev 0x7FEC21C03AA0, Data 0
 5: Node 0x7FEC21C03AE0, Next 0x000000000000, Prev 0x7FEC21C03AC0, Data 4
List Split-L (0x7FEC21C03B40)
Head 0x7FEC21C03A60, Tail 0x7FEC21C03AA0, Size 3
 1: Node 0x7FEC21C03A60, Next 0x7FEC21C03A80, Prev 0x000000000000, Data 5
 2: Node 0x7FEC21C03A80, Next 0x7FEC21C03AA0, Prev 0x7FEC21C03A60, Data 8
 3: Node 0x7FEC21C03AA0, Next 0x000000000000, Prev 0x7FEC21C03A80, Data 6
List Split-R (0x7FEC21C03B60)
Head 0x7FEC21C03AC0, Tail 0x7FEC21C03AE0, Size 2
 1: Node 0x7FEC21C03AC0, Next 0x7FEC21C03AE0, Prev 0x000000000000, Data 0
 2: Node 0x7FEC21C03AE0, Next 0x000000000000, Prev 0x7FEC21C03AC0, Data 4
List -->>list_sort_merge() (0x7FEC21C03B40)
Head 0x7FEC21C03A60, Tail 0x7FEC21C03AA0, Size 3
 1: Node 0x7FEC21C03A60, Next 0x7FEC21C03A80, Prev 0x000000000000, Data 5
 2: Node 0x7FEC21C03A80, Next 0x7FEC21C03AA0, Prev 0x7FEC21C03A60, Data 8
 3: Node 0x7FEC21C03AA0, Next 0x000000000000, Prev 0x7FEC21C03A80, Data 6
List Split-L (0x7FEC21C03BA0)
Head 0x7FEC21C03A60, Tail 0x7FEC21C03A80, Size 2
 1: Node 0x7FEC21C03A60, Next 0x7FEC21C03A80, Prev 0x000000000000, Data 5
 2: Node 0x7FEC21C03A80, Next 0x000000000000, Prev 0x7FEC21C03A60, Data 8
List Split-R (0x7FEC21C03B80)
Head 0x7FEC21C03AA0, Tail 0x7FEC21C03AA0, Size 1
 1: Node 0x7FEC21C03AA0, Next 0x000000000000, Prev 0x000000000000, Data 6
List -->>list_sort_merge() (0x7FEC21C03BA0)
Head 0x7FEC21C03A60, Tail 0x7FEC21C03A80, Size 2
 1: Node 0x7FEC21C03A60, Next 0x7FEC21C03A80, Prev 0x000000000000, Data 5
 2: Node 0x7FEC21C03A80, Next 0x000000000000, Prev 0x7FEC21C03A60, Data 8
List Split-L (0x7FEC21C03BE0)
Head 0x7FEC21C03A60, Tail 0x7FEC21C03A60, Size 1
 1: Node 0x7FEC21C03A60, Next 0x000000000000, Prev 0x000000000000, Data 5
List Split-R (0x7FEC21C03BC0)
Head 0x7FEC21C03A80, Tail 0x7FEC21C03A80, Size 1
 1: Node 0x7FEC21C03A80, Next 0x000000000000, Prev 0x000000000000, Data 8
-->>list_sort_merge()
List List-L (0x7FEC21C03BE0)
Head 0x7FEC21C03A60, Tail 0x7FEC21C03A60, Size 1
 1: Node 0x7FEC21C03A60, Next 0x000000000000, Prev 0x000000000000, Data 5
List List-R (0x7FEC21C03BC0)
Head 0x7FEC21C03A80, Tail 0x7FEC21C03A80, Size 1
 1: Node 0x7FEC21C03A80, Next 0x000000000000, Prev 0x000000000000, Data 8
<<--list_sort_merge()
List <<--list_sort_merge() (0x7FEC21C03BA0)
Head 0x7FEC21C03A80, Tail 0x7FEC21C03A60, Size 2
 1: Node 0x7FEC21C03A80, Next 0x7FEC21C03A60, Prev 0x000000000000, Data 8
 2: Node 0x7FEC21C03A60, Next 0x000000000000, Prev 0x7FEC21C03A80, Data 5
-->>list_sort_merge()
List List-L (0x7FEC21C03BA0)
Head 0x7FEC21C03A80, Tail 0x7FEC21C03A60, Size 2
 1: Node 0x7FEC21C03A80, Next 0x7FEC21C03A60, Prev 0x000000000000, Data 8
 2: Node 0x7FEC21C03A60, Next 0x000000000000, Prev 0x7FEC21C03A80, Data 5
List List-R (0x7FEC21C03B80)
Head 0x7FEC21C03AA0, Tail 0x7FEC21C03AA0, Size 1
 1: Node 0x7FEC21C03AA0, Next 0x000000000000, Prev 0x000000000000, Data 6
<<--list_sort_merge()
List <<--list_sort_merge() (0x7FEC21C03B40)
Head 0x7FEC21C03A80, Tail 0x7FEC21C03A60, Size 3
 1: Node 0x7FEC21C03A80, Next 0x7FEC21C03AA0, Prev 0x000000000000, Data 8
 2: Node 0x7FEC21C03AA0, Next 0x7FEC21C03A60, Prev 0x7FEC21C03A80, Data 6
 3: Node 0x7FEC21C03A60, Next 0x000000000000, Prev 0x7FEC21C03AA0, Data 5
List -->>list_sort_merge() (0x7FEC21C03B60)
Head 0x7FEC21C03AC0, Tail 0x7FEC21C03AE0, Size 2
 1: Node 0x7FEC21C03AC0, Next 0x7FEC21C03AE0, Prev 0x000000000000, Data 0
 2: Node 0x7FEC21C03AE0, Next 0x000000000000, Prev 0x7FEC21C03AC0, Data 4
List Split-L (0x7FEC21C03B80)
Head 0x7FEC21C03AC0, Tail 0x7FEC21C03AC0, Size 1
 1: Node 0x7FEC21C03AC0, Next 0x000000000000, Prev 0x000000000000, Data 0
List Split-R (0x7FEC21C03BA0)
Head 0x7FEC21C03AE0, Tail 0x7FEC21C03AE0, Size 1
 1: Node 0x7FEC21C03AE0, Next 0x000000000000, Prev 0x000000000000, Data 4
-->>list_sort_merge()
List List-L (0x7FEC21C03B80)
Head 0x7FEC21C03AC0, Tail 0x7FEC21C03AC0, Size 1
 1: Node 0x7FEC21C03AC0, Next 0x000000000000, Prev 0x000000000000, Data 0
List List-R (0x7FEC21C03BA0)
Head 0x7FEC21C03AE0, Tail 0x7FEC21C03AE0, Size 1
 1: Node 0x7FEC21C03AE0, Next 0x000000000000, Prev 0x000000000000, Data 4
<<--list_sort_merge()
List <<--list_sort_merge() (0x7FEC21C03B60)
Head 0x7FEC21C03AE0, Tail 0x7FEC21C03AC0, Size 2
 1: Node 0x7FEC21C03AE0, Next 0x7FEC21C03AC0, Prev 0x000000000000, Data 4
 2: Node 0x7FEC21C03AC0, Next 0x000000000000, Prev 0x7FEC21C03AE0, Data 0
-->>list_sort_merge()
List List-L (0x7FEC21C03B40)
Head 0x7FEC21C03A80, Tail 0x7FEC21C03A60, Size 3
 1: Node 0x7FEC21C03A80, Next 0x7FEC21C03AA0, Prev 0x000000000000, Data 8
 2: Node 0x7FEC21C03AA0, Next 0x7FEC21C03A60, Prev 0x7FEC21C03A80, Data 6
 3: Node 0x7FEC21C03A60, Next 0x000000000000, Prev 0x7FEC21C03AA0, Data 5
List List-R (0x7FEC21C03B60)
Head 0x7FEC21C03AE0, Tail 0x7FEC21C03AC0, Size 2
 1: Node 0x7FEC21C03AE0, Next 0x7FEC21C03AC0, Prev 0x000000000000, Data 4
 2: Node 0x7FEC21C03AC0, Next 0x000000000000, Prev 0x7FEC21C03AE0, Data 0
<<--list_sort_merge()
List <<--list_sort_merge() (0x7FEC21C03B00)
Head 0x7FEC21C03A80, Tail 0x7FEC21C03AC0, Size 5
 1: Node 0x7FEC21C03A80, Next 0x7FEC21C03AA0, Prev 0x000000000000, Data 8
 2: Node 0x7FEC21C03AA0, Next 0x7FEC21C03A60, Prev 0x7FEC21C03A80, Data 6
 3: Node 0x7FEC21C03A60, Next 0x7FEC21C03AE0, Prev 0x7FEC21C03AA0, Data 5
 4: Node 0x7FEC21C03AE0, Next 0x7FEC21C03AC0, Prev 0x7FEC21C03A60, Data 4
 5: Node 0x7FEC21C03AC0, Next 0x000000000000, Prev 0x7FEC21C03AE0, Data 0
-->>list_sort_merge()
List List-L (0x7FEC21C03B20)
Head 0x7FEC21C03A00, Tail 0x7FEC21C039C0, Size 5
 1: Node 0x7FEC21C03A00, Next 0x7FEC21C03A40, Prev 0x000000000000, Data 9
 2: Node 0x7FEC21C03A40, Next 0x7FEC21C039E0, Prev 0x7FEC21C03A00, Data 7
 3: Node 0x7FEC21C039E0, Next 0x7FEC21C03A20, Prev 0x7FEC21C03A40, Data 3
 4: Node 0x7FEC21C03A20, Next 0x7FEC21C039C0, Prev 0x7FEC21C039E0, Data 2
 5: Node 0x7FEC21C039C0, Next 0x000000000000, Prev 0x7FEC21C03A20, Data 1
List List-R (0x7FEC21C03B00)
Head 0x7FEC21C03A80, Tail 0x7FEC21C03AC0, Size 5
 1: Node 0x7FEC21C03A80, Next 0x7FEC21C03AA0, Prev 0x000000000000, Data 8
 2: Node 0x7FEC21C03AA0, Next 0x7FEC21C03A60, Prev 0x7FEC21C03A80, Data 6
 3: Node 0x7FEC21C03A60, Next 0x7FEC21C03AE0, Prev 0x7FEC21C03AA0, Data 5
 4: Node 0x7FEC21C03AE0, Next 0x7FEC21C03AC0, Prev 0x7FEC21C03A60, Data 4
 5: Node 0x7FEC21C03AC0, Next 0x000000000000, Prev 0x7FEC21C03AE0, Data 0
<<--list_sort_merge()
List <<--list_sort_merge() (0x7FEC21C039A0)
Head 0x7FEC21C03A00, Tail 0x7FEC21C03AC0, Size 10
 1: Node 0x7FEC21C03A00, Next 0x7FEC21C03A80, Prev 0x000000000000, Data 9
 2: Node 0x7FEC21C03A80, Next 0x7FEC21C03A40, Prev 0x7FEC21C03A00, Data 8
 3: Node 0x7FEC21C03A40, Next 0x7FEC21C03AA0, Prev 0x7FEC21C03A80, Data 7
 4: Node 0x7FEC21C03AA0, Next 0x7FEC21C03A60, Prev 0x7FEC21C03A40, Data 6
 5: Node 0x7FEC21C03A60, Next 0x7FEC21C03AE0, Prev 0x7FEC21C03AA0, Data 5
 6: Node 0x7FEC21C03AE0, Next 0x7FEC21C039E0, Prev 0x7FEC21C03A60, Data 4
 7: Node 0x7FEC21C039E0, Next 0x7FEC21C03A20, Prev 0x7FEC21C03AE0, Data 3
 8: Node 0x7FEC21C03A20, Next 0x7FEC21C039C0, Prev 0x7FEC21C039E0, Data 2
 9: Node 0x7FEC21C039C0, Next 0x7FEC21C03AC0, Prev 0x7FEC21C03A20, Data 1
10: Node 0x7FEC21C03AC0, Next 0x000000000000, Prev 0x7FEC21C039C0, Data 0
List After (0x7FEC21C039A0)
Head 0x7FEC21C03A00, Tail 0x7FEC21C03AC0, Size 10
 1: Node 0x7FEC21C03A00, Next 0x7FEC21C03A80, Prev 0x000000000000, Data 9
 2: Node 0x7FEC21C03A80, Next 0x7FEC21C03A40, Prev 0x7FEC21C03A00, Data 8
 3: Node 0x7FEC21C03A40, Next 0x7FEC21C03AA0, Prev 0x7FEC21C03A80, Data 7
 4: Node 0x7FEC21C03AA0, Next 0x7FEC21C03A60, Prev 0x7FEC21C03A40, Data 6
 5: Node 0x7FEC21C03A60, Next 0x7FEC21C03AE0, Prev 0x7FEC21C03AA0, Data 5
 6: Node 0x7FEC21C03AE0, Next 0x7FEC21C039E0, Prev 0x7FEC21C03A60, Data 4
 7: Node 0x7FEC21C039E0, Next 0x7FEC21C03A20, Prev 0x7FEC21C03AE0, Data 3
 8: Node 0x7FEC21C03A20, Next 0x7FEC21C039C0, Prev 0x7FEC21C039E0, Data 2
 9: Node 0x7FEC21C039C0, Next 0x7FEC21C03AC0, Prev 0x7FEC21C03A20, Data 1
10: Node 0x7FEC21C03AC0, Next 0x000000000000, Prev 0x7FEC21C039C0, Data 0

`mergelist.c`

splitlist()中最大的问题是列表没有被彻底切断。如果您追踪左侧列表，则也会遍历右侧列表。这可能会导致问题 - 事实上很多问题。

#include "list.h"
#include <assert.h>

static void mergelist(list_t *list_ptr, list_t *left_list, list_t *right_list);
static void splitlist(list_t *list_ptr, list_t *left_list, list_t *right_list);

static int comp_proc(data_t d1, data_t d2)
{
    if (d1 > d2)
        return +1;
    else if (d1 < d2)
        return -1;
    else
        return 0;
}

void list_sort_merge(list_t *list_ptr)
{
    if (list_ptr->size > 1)  // 1, not 0 — do not try splitting a singleton list.
    {
        dump_list(stdout, "-->>list_sort_merge()", list_ptr);  // Debug
        list_t *right_list = list_construct();
        list_t *left_list = list_construct();
        splitlist(list_ptr, left_list, right_list);
        dump_list(stdout, "Split-L", left_list);  // Debug
        dump_list(stdout, "Split-R", right_list); // Debug
        list_sort_merge(left_list);
        list_sort_merge(right_list);
        dump_list(stdout, "Sort-L", left_list);  // Debug
        dump_list(stdout, "Sort-R", right_list); // Debug
        list_ptr->head = NULL;
        list_ptr->tail = NULL;
        list_ptr->size = 0;    // Additional
        mergelist(list_ptr, left_list, right_list);
        list_destruct(right_list);
        list_destruct(left_list);
        dump_list(stdout, "<<--list_sort_merge()", list_ptr); // Debug
    }
}

static void mergelist(list_t *list_ptr, list_t *left_list, list_t *right_list)
{
    node_t *holder;
    fprintf(stdout, "-->>list_sort_merge()\n");
    dump_list(stdout, "List-L", left_list);
    dump_list(stdout, "List-R", right_list);
    while (left_list->size > 0 && right_list->size > 0)
    {
        assert(left_list->head != 0 && right_list->head != 0);
        /* Sort into descending order */
        if (comp_proc(left_list->head->data, right_list->head->data) > 0)
        {
            holder = list_remove_head(left_list);
            list_insert_tail(list_ptr, holder);
        }
        else
        {
            holder = list_remove_head(right_list);
            list_insert_tail(list_ptr, holder);
        }
    }
    while (left_list->size > 0)
    {
        holder = list_remove_head(left_list);
        list_insert_tail(list_ptr, holder);
    }
    while (right_list->size > 0)
    {
        holder = list_remove_head(right_list);
        list_insert_tail(list_ptr, holder);
    }
    fprintf(stdout, "<<--list_sort_merge()\n");
}

static void splitlist(list_t *list_ptr, list_t *left_list, list_t *right_list)
{
    if (list_ptr->size > 1)
    {
        size_t temp = 0;
        node_t *holder = list_ptr->head;
        right_list->size = list_ptr->size / 2;
        left_list->size = list_ptr->size - right_list->size;

        left_list->head = list_ptr->head;
        right_list->tail = list_ptr->tail;

        while (temp < left_list->size)
        {
            temp++;
            holder = holder->next;
        }

        /* Make sure the two lists are separate — a major issue */
        right_list->head = holder;
        left_list->tail = holder->prev;
        left_list->tail->next = NULL;
        left_list->head->prev = NULL;
        right_list->tail->next = NULL;
        right_list->head->prev = NULL;
    }
}

int main(void)
{
    int values[] = { 1, 3, 9, 2, 7, 5, 8, 6, 0, 4 };
    enum { NUM_VALUES = sizeof(values)/sizeof(values[0]) };
    list_t *list = list_construct();

    //dump_list(stdout, "Empty list", list);
    for (size_t i = 0; i < NUM_VALUES; i++)
    {
        node_t *node = node_construct(values[i]);
        list_insert_tail(list, node);
        //dump_list(stdout, "Inserting", list);
    }

    dump_list(stdout, "Before", list);
    list_sort_merge(list);
    dump_list(stdout, "After", list);

    list_destruct(list);

    return 0;
}

`list.h`

#ifndef LIST_H_INCLUDED
#define LIST_H_INCLUDED

#include <stdio.h>

typedef int data_t;

typedef struct node_t node_t;
struct node_t
{
    node_t *next;
    node_t *prev;
    data_t  data;
};

typedef struct list_t list_t;
struct list_t
{
    node_t *head;
    node_t *tail;
    size_t  size;
};

extern node_t *node_construct(data_t data);
extern void    node_destruct(node_t *node);

extern size_t  list_size(list_t *list);
extern void    list_insert_tail(list_t *list, node_t *node);
extern node_t *list_remove_head(list_t *list);
extern void    list_destruct(list_t *list);
extern list_t *list_construct(void);
extern void    dump_list(FILE *fp, const char *tag, list_t *list);

extern void list_sort_merge(list_t *list_ptr);

#endif /* LIST_H_INCLUDED */

`list.c`

#include "list.h"
#include <assert.h>
#include <inttypes.h>
#include <stdlib.h>

extern node_t *list_head(list_t *list);
extern node_t *list_tail(list_t *list);
extern void    list_destruct(list_t *list);
extern list_t *list_construct(void);

size_t list_size(list_t *list)
{
    return list->size;
}

void list_insert_tail(list_t *list, node_t *node)
{
    assert(list != 0);
    assert(node != 0);
    if (list->tail == 0)
    {
        assert(list->tail == 0 && list->head == 0 && list->size == 0);
        list->tail = node;
        list->head = node;
        node->prev = 0;
        node->next = 0;
        list->size = 1;
    }
    else
    {
        list->tail->next = node;
        node->prev = list->tail;
        node->next = 0;
        list->size++;
        list->tail = node;
    }
}

node_t *list_remove_head(list_t *list)
{
    assert(list != 0);
    node_t *node = list->head;
    if (list->head != 0)
    {
        assert(list->size > 0);
        list->head = node->next;
        if (node->next != 0)
            node->next->prev = 0;
        node->prev = 0;
        node->next = 0;
        list->size--;
    }
    return node;
}

void list_destruct(list_t *list)
{
    assert(list != 0);
    node_t *next;
    for (node_t *node = list->head; node != 0; node = next)
    {
        next = node->next;
        node_destruct(node);
    }
    free(list);
}

void dump_list(FILE *fp, const char *tag, list_t *list)
{
    assert(list != 0);
    fprintf(fp, "List %s (0x%.12" PRIXPTR ")\n", tag, (uintptr_t)list);
    fprintf(fp, "Head 0x%.12" PRIXPTR ", Tail 0x%.12" PRIXPTR ", Size %zu\n",
            (uintptr_t)list->head, (uintptr_t)list->tail, list->size);
    size_t i = 0;
    for (node_t *node = list->head; node != 0; node = node->next)
        fprintf(fp, "%2zu: Node 0x%.12" PRIXPTR ", Next 0x%.12" PRIXPTR ", Prev 0x%.12" PRIXPTR ", Data %d\n",
            ++i, (uintptr_t)node, (uintptr_t)node->next, (uintptr_t)node->prev, node->data);
}

list_t *list_construct(void)
{
    list_t *list = malloc(sizeof(*list));
    if (list != 0)
    {
        list->head = 0;
        list->tail = 0;
        list->size = 0;
    }
    return list;
}

node_t *node_construct(data_t data)
{
    node_t *node = malloc(sizeof(*node));
    if (node != 0)
    {
        node->data = data;
        node->next = 0;
        node->prev = 0;
    }
    return node;
}

void node_destruct(node_t *node)
{
    free(node);
}

使用mergesort对链接列表进行排序

2 个答案:

示例输出

`mergelist.c`

`list.h`

`list.c`