我编写了一个小型c程序，该程序以3个名称作为输入，然后将这三个值存储到节点。这三个值（名称）存储在数组JOHNJAKEMATT中，每个名称都有4个字符。生成的Node看起来像这样：
/*
pointer_to_linked_list
|
v
node[2] node[1] node[0]
| | |
| | |
+------+---+ +------+---+ +-------+------+
| MATT | o-----> | JAKE | o--------> | JOHN | NULL |
+------+---+ +------+---+ +-------+------+
*/
一切正常，一切都按预期进行。
每个名称都临时存储在数组中，然后移动到节点中的data。为此，我分配了内存，如果出现故障，我编写了一个函数，如果内存分配失败，该函数应释放所有内存：
void freeNode(struct _Node_ *current_node)
{
struct _Node_ *tmp_node;
while(current_node != NULL) {
tmp_node = current_node;
current_node = current_node->next;
free(tmp_node);
}
return;
}
我还写了一个函数，可以打印出我的链表：
void printNodes(struct _Node_ *current_node) {
while(current_node != NULL) {
printf("%s\n", current_node->data);
current_node = current_node->next;
}
}
控制台中的结果是带有每个值的链表：
MATT
JAKE
JOHN
一切正常，然后我想用valgrind（valgrind --leak-check=yes --track-origins=yes ./main）检查是否存在任何错误-是的，存在两种错误类型：
完整的valgrind报告：
==20043== Memcheck, a memory error detector
==20043== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==20043== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
==20043== Command: ./main
==20043==
MATT
==20043== Conditional jump or move depends on uninitialised value(s)
==20043== at 0x1094BC: printNodes (in /home/osboxes/Dropbox/ESP/main)
==20043== by 0x10928F: main (in /home/osboxes/Dropbox/ESP/main)
==20043== Uninitialised value was created by a stack allocation
==20043== at 0x10935C: saveToLinkedList (in /home/osboxes/Dropbox/ESP/main)
==20043==
==20043== Use of uninitialised value of size 8
==20043== at 0x1094A0: printNodes (in /home/osboxes/Dropbox/ESP/main)
==20043== by 0x10928F: main (in /home/osboxes/Dropbox/ESP/main)
==20043== Uninitialised value was created by a stack allocation
==20043== at 0x10935C: saveToLinkedList (in /home/osboxes/Dropbox/ESP/main)
==20043==
JAKE
==20043== Use of uninitialised value of size 8
==20043== at 0x1094AF: printNodes (in /home/osboxes/Dropbox/ESP/main)
==20043== by 0x10928F: main (in /home/osboxes/Dropbox/ESP/main)
==20043== Uninitialised value was created by a stack allocation
==20043== at 0x10935C: saveToLinkedList (in /home/osboxes/Dropbox/ESP/main)
==20043==
JOHN
==20043== Conditional jump or move depends on uninitialised value(s)
==20043== at 0x1094F4: freeNode (in /home/osboxes/Dropbox/ESP/main)
==20043== by 0x10929B: main (in /home/osboxes/Dropbox/ESP/main)
==20043== Uninitialised value was created by a stack allocation
==20043== at 0x10935C: saveToLinkedList (in /home/osboxes/Dropbox/ESP/main)
==20043==
==20043== Use of uninitialised value of size 8
==20043== at 0x1094DB: freeNode (in /home/osboxes/Dropbox/ESP/main)
==20043== by 0x10929B: main (in /home/osboxes/Dropbox/ESP/main)
==20043== Uninitialised value was created by a stack allocation
==20043== at 0x10935C: saveToLinkedList (in /home/osboxes/Dropbox/ESP/main)
==20043==
==20043== Conditional jump or move depends on uninitialised value(s)
==20043== at 0x4838931: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==20043== by 0x1094EE: freeNode (in /home/osboxes/Dropbox/ESP/main)
==20043== by 0x10929B: main (in /home/osboxes/Dropbox/ESP/main)
==20043== Uninitialised value was created by a stack allocation
==20043== at 0x10935C: saveToLinkedList (in /home/osboxes/Dropbox/ESP/main)
==20043==
==20043==
==20043== HEAP SUMMARY:
==20043== in use at exit: 15 bytes in 3 blocks
==20043== total heap usage: 7 allocs, 4 frees, 1,087 bytes allocated
==20043==
==20043== 5 bytes in 1 blocks are definitely lost in loss record 1 of 2
==20043== at 0x483774F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==20043== by 0x1091D4: copyToNewNode (in /home/osboxes/Dropbox/ESP/main)
==20043== by 0x10942E: saveToLinkedList (in /home/osboxes/Dropbox/ESP/main)
==20043== by 0x10932F: readInput (in /home/osboxes/Dropbox/ESP/main)
==20043== by 0x109271: main (in /home/osboxes/Dropbox/ESP/main)
==20043==
==20043== 10 bytes in 2 blocks are definitely lost in loss record 2 of 2
==20043== at 0x483774F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==20043== by 0x1091D4: copyToNewNode (in /home/osboxes/Dropbox/ESP/main)
==20043== by 0x109459: saveToLinkedList (in /home/osboxes/Dropbox/ESP/main)
==20043== by 0x10932F: readInput (in /home/osboxes/Dropbox/ESP/main)
==20043== by 0x109271: main (in /home/osboxes/Dropbox/ESP/main)
==20043==
==20043== LEAK SUMMARY:
==20043== definitely lost: 15 bytes in 3 blocks
==20043== indirectly lost: 0 bytes in 0 blocks
==20043== possibly lost: 0 bytes in 0 blocks
==20043== still reachable: 0 bytes in 0 blocks
==20043== suppressed: 0 bytes in 0 blocks
==20043==
==20043== For counts of detected and suppressed errors, rerun with: -v
==20043== ERROR SUMMARY: 14 errors from 8 contexts (suppressed: 0 from 0)
main.c的完整代码：
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct _Node_
{
char *data;
struct _Node_ *next;
};
struct _Node_ *copyToNewNode(char *pointer_value_linked_list, struct _Node_ *nextnode);
struct _Node_ *readInput(char *pointer_buffer_config, int len_char);
struct _Node_ *saveToLinkedList(char *pointer_tmp_buffer, int str_len, int pos_node);
void printNodes(struct _Node_ *current_node);
void freeNode(struct _Node_ *current_node);
struct _Node_ *copyToNewNode(char *pointer_value_linked_list, struct _Node_ *nextnode)
{
struct _Node_ *new_node_pointer;
new_node_pointer = malloc(sizeof(struct _Node_));
if (!new_node_pointer)
{
freeNode(new_node_pointer);
return NULL;
}
new_node_pointer->data = malloc(strlen(pointer_value_linked_list) + 1);
if (!new_node_pointer->data)
{
freeNode(new_node_pointer);
return NULL;
}
strcpy(new_node_pointer->data,pointer_value_linked_list);
new_node_pointer->next = nextnode;
return(new_node_pointer);
}
int main()
{
char buffer_config[] = "JOHNJAKEMATT";
struct _Node_ *pointer_to_linked_list;
pointer_to_linked_list = readInput(buffer_config, strlen(buffer_config));
if(pointer_to_linked_list == NULL)
{
//nodes have already been freed
return 0;
}
printNodes(pointer_to_linked_list);
freeNode(pointer_to_linked_list);
return 1;
}
struct _Node_ *readInput(char *pointer_buffer_config, int len_char)
{
char tmp_buffer_input[5];
int counter;
struct _Node_ *pointer_last_node; // points to last successful saved node
int pos_node = 0;
int counter_next_node = 0;
while(counter_next_node != 3)
{
for(counter = 0; counter < 4; counter++)
{
tmp_buffer_input[counter] = *pointer_buffer_config;
pointer_buffer_config++;
}
tmp_buffer_input[4] = '\0';
pointer_last_node = saveToLinkedList(tmp_buffer_input, strlen(tmp_buffer_input), pos_node);
++pos_node;
counter_next_node++;
}
return pointer_last_node;
}
struct _Node_ *saveToLinkedList(char *pointer_tmp_buffer, int str_len, int pos_node)
{
char value_linked_list[str_len+1];
int counter = 0;
while(counter != str_len)
{
value_linked_list[counter] = *(pointer_tmp_buffer+counter);
counter++;
}
value_linked_list[counter] = '\0';
struct _Node_* node[3];
if(pos_node == 0)
{
node[pos_node] = copyToNewNode(value_linked_list, NULL);
}
else
{
node[pos_node] = copyToNewNode(value_linked_list, node[pos_node-1]);
}
return node[pos_node];
}
void printNodes(struct _Node_ *current_node) {
while(current_node != NULL) {
printf("%s\n", current_node->data);
current_node = current_node->next;
}
}
void freeNode(struct _Node_ *current_node)
{
struct _Node_ *tmp_node;
while(current_node != NULL) {
tmp_node = current_node;
current_node = current_node->next;
free(tmp_node);
}
return;
}
即使有人在阅读了valgrind手册后我也不知道错误可能在哪里，如果有人可以帮助我定位此错误，我将非常感激。 谢谢。
答案 0 :(得分：3)
进入saveToLinkedList
struct _Node_* node[3];
if(pos_node == 0)
{
node[pos_node] = copyToNewNode(value_linked_list, NULL);
}
else
{
node[pos_node] = copyToNewNode(value_linked_list, node[pos_node-1]);
}
struct _Node_* node[3]未初始化，当pos_node不为0时，您将使用未初始化向量的条目=> copyToNewNode将创建带有随机下一个指针的节点
struct _Node_* node[3];必须为static struct _Node_* node[3];
在freeNode()中，您错过了释放字段数据的过程，必须像：
void freeNode(struct _Node_ *current_node)
{
struct _Node_ *tmp_node;
while(current_node != NULL) {
tmp_node = current_node;
current_node = current_node->next;
if (tmp_node->data != NULL)
free(tmp_node->data);
free(tmp_node);
}
}