好的伙计们，在 gdb 和 valgrind 没有成功之后，我谦虚地向您提出我的问题。我们被要求在 c 中实现一个版本的快速排序，使用列表的第一个元素作为枢轴（以保持与我们在学期早些时候所做的简单 haskell 实现的可比性）。提供了 LIST 实现（制作、打印和结构定义），其余的取决于我们。我（惊讶，惊讶）收到一个段错误，但 valgrind 出现了大量错误以及堆栈溢出，所以也许一些新鲜的眼睛可以帮助我。
我的代码：
#include <stdio.h>
#include <stdlib.h>
typedef struct CELL *LIST;
struct CELL {
int element;
LIST next;
};
LIST MakeList();
void PrintList(LIST);
LIST qSort(LIST);
int listLength(LIST);
LIST combine(LIST, LIST, LIST);
int main(){
LIST list;
printf ("enter a several numbers separated by spaces or returns and ended by Ctrl-Dn");
list = MakeList();
PrintList(qSort(list));
return 0;
}
LIST qSort(LIST list){
LIST current, pivot = list, temp = NULL;//use first element as pivot, start comparison at list->next
LIST little, big, littleHead, bigHead;
little = (LIST) malloc(sizeof(struct CELL));
little->element = 0;
little->next = NULL;
littleHead = little;
big = (LIST) malloc(sizeof(struct CELL));
big->element = 0;
big->next = NULL;
bigHead = big;
if(listLength(list) <= 1){//base case
return list;
}
//remove pivot by setting current to list->next
current = list->next;
do{
if(current->element <= pivot->element){
little->element = current->element;
little->next = (LIST) malloc(sizeof(struct CELL));
little = little->next;
little->next = NULL;
}
else{
big->element = current->element;
big->next = (LIST) malloc(sizeof(struct CELL));
big = big->next;
big->next = NULL;
}
current = current->next;
}while(current != NULL);
littleHead = qSort(littleHead);
bigHead = qSort(bigHead);
return combine(littleHead, bigHead, pivot);
}
int listLength(LIST list){
int length = 0;
LIST current = list;
if(NULL==list){
return length;
}
else{
while(current != NULL){
current = current->next;
length++;
}
}
return length;
}
LIST combine(LIST little, LIST big, LIST pivot){
LIST temp = little;
while(temp->next != NULL){
temp = temp->next;
}
temp->next = pivot;
pivot->next = big;
return little;
}
LIST MakeList()
{
int x;
LIST pNewCell;
if (scanf("%d", &x) == EOF) return NULL;
else {
pNewCell = (LIST) malloc(sizeof(struct CELL));
pNewCell->next = MakeList();
pNewCell->element = x;
return pNewCell;
}
}
void PrintList(LIST list)
{
while (list != NULL) {
printf("%dn", list->element);
list = list->next;
}
}
和瓦尔格林德输出
==20391== Conditional jump or move depends on uninitialised value(s)
==20391== at 0x804855D: qSort (2100assignment4.c:45)
==20391== by 0x80485E0: qSort (2100assignment4.c:61)
==20391== by 0x80484BD: main (2100assignment4.c:22)
==20391== Uninitialised value was created by a heap allocation
==20391== at 0x402BE68: malloc (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==20391== by 0x8048574: qSort (2100assignment4.c:47)
==20391== by 0x80484BD: main (2100assignment4.c:22)
==20391==
==20391== Conditional jump or move depends on uninitialised value(s)
==20391== at 0x804855D: qSort (2100assignment4.c:45)
==20391== by 0x80485E0: qSort (2100assignment4.c:61)
==20391== by 0x80485E0: qSort (2100assignment4.c:61)
==20391== by 0x80484BD: main (2100assignment4.c:22)
==20391== Uninitialised value was created by a heap allocation
==20391== at 0x402BE68: malloc (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==20391== by 0x8048574: qSort (2100assignment4.c:47)
==20391== by 0x80484BD: main (2100assignment4.c:22)
==20391==
==20391== Conditional jump or move depends on uninitialised value(s)
==20391== at 0x804855D: qSort (2100assignment4.c:45)
==20391== by 0x80485E0: qSort (2100assignment4.c:61)
==20391== by 0x80485E0: qSort (2100assignment4.c:61)
==20391== by 0x80485E0: qSort (2100assignment4.c:61)
==20391== by 0x80484BD: main (2100assignment4.c:22)
==20391== Uninitialised value was created by a heap allocation
==20391== at 0x402BE68: malloc (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==20391== by 0x8048574: qSort (2100assignment4.c:47)
==20391== by 0x80485E0: qSort (2100assignment4.c:61)
==20391== by 0x80484BD: main (2100assignment4.c:22)
==20391==
==20391== Stack overflow in thread 1: can't grow stack to 0xbe297ff4
==20391==
==20391== Process terminating with default action of signal 11 (SIGSEGV)
==20391== Access not within mapped region at address 0xBE297FF4
==20391== at 0x402BE35: malloc (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==20391== If you believe this happened as a result of a stack
==20391== overflow in your program's main thread (unlikely but
==20391== possible), you can try to increase the size of the
==20391== main thread stack using the --main-stacksize= flag.
==20391== The main thread stack size used in this run was 8388608.
==20391== Stack overflow in thread 1: can't grow stack to 0xbe297fe4
==20391==
==20391== Process terminating with default action of signal 11 (SIGSEGV)
==20391== Access not within mapped region at address 0xBE297FE4
==20391== at 0x4025430: _vgnU_freeres (in /usr/lib/valgrind/vgpreload_core-x86-linux.so)
==20391== If you believe this happened as a result of a stack
==20391== overflow in your program's main thread (unlikely but
==20391== possible), you can try to increase the size of the
==20391== main thread stack using the --main-stacksize= flag.
==20391== The main thread stack size used in this run was 8388608.
==20391==
==20391== HEAP SUMMARY:
==20391== in use at exit: 4,190,952 bytes in 523,869 blocks
==20391== total heap usage: 523,869 allocs, 0 frees, 4,190,952 bytes allocated
==20391==
==20391== LEAK SUMMARY:
==20391== definitely lost: 0 bytes in 0 blocks
==20391== indirectly lost: 0 bytes in 0 blocks
==20391== possibly lost: 0 bytes in 0 blocks
==20391== still reachable: 4,190,952 bytes in 523,869 blocks
==20391== suppressed: 0 bytes in 0 blocks
==20391== Rerun with --leak-check=full to see details of leaked memory
==20391==
==20391== For counts of detected and suppressed errors, rerun with: -v
==20391== ERROR SUMMARY: 261929 errors from 3 contexts (suppressed: 0 from 0)
首先要解决的一些问题：
if (scanf("%d", &x) == EOF) return NULL;
\。检查 ！= 1 可能更容易，因为您期望一个值。
这导致您的 MakeList 无限递归（至少在我的机器上）。
在你的 qsort 函数中，你的小列表和大列表的末尾总是有一个虚拟条目 - 由这个代码完成
little->next = (LIST) malloc(sizeof(struct CELL));
little = little->next;
little->next = NULL;
这意味着当您拆分列表时，您最终的条目总是比开始时多，因此它永远不会完成。另请注意，这些新条目没有设置其元素值，这可能是您收到未初始化警告的地方。
您应该重新考虑如何存储子列表，也许将它们作为 NULL 开始，以指示空，尽管这将使添加新值变得更加困难。
您可以按如下方式编辑您的makelist函数。
您将观察到很少的变化。
- 删除
scanf是正确的（参考黑暗的答案）scanf读入，这将确保如果您输入任何不兼容的输入（如任何字母而不是 Ctrl + D），读取将停止。
LIST MakeList()
{
int x;
LIST pNewCell;
while(scanf("%d", &x))
{
pNewCell = (LIST) malloc(sizeof(struct CELL));
pNewCell->next = MakeList();
pNewCell->element = x;
return pNewCell;
}
return NULL;
}