我正在编写一个链表，其中包含一个节点的结构和一个列表的结构，我遇到了一个问题，当我malloc一个新节点时，它具有与list->head相同的地址，因此过度写入列表头使列表错误。
驱动程序.c
#include "target.h"
int main(int argc, char * argv[]){
struct target_list * target = target_list_alloc("list");
target_list_print(target);
target_list_append(target, "G");
target_list_append(target, "B");
target_list_print(target);
target_list_append(target, "S");
target_list_print(target);
target_list_remove(target,"B");
target_list_print(target);
target_list_remove(target,"Bl");
target_list_remove(target,"Br");
target_list_print(target);
target_list_append(target,"Ba"); //Here is the problem node
target_list_print(target);
return 0;
}
目标.h
#ifndef TARGET_H
#define TARGET_H
#include <stdbool.h>
#include <stdio.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>
/*-----------------------------------------*/
extern char * prog;
/*-----------------------------------------*/
struct source_list{
char * name;
};
struct recipe_list{
char * name;
};
struct target_node{
char * name;
struct target_node * next;
struct source_list * src_list;
struct recipe_list * rec_list;
};
struct target_list{
char * name;
struct target_node * head;
struct target_node * tail;
};
/*-----------------------------------------------------*/
void target_list_init(struct target_list * list, const char * targetname);
struct target_list * target_list_alloc(const char * targetname);
void target_list_deallocate(struct target_list * list);
void target_list_print(struct target_list * list);
void target_list_append(struct target_list * list, const char * nodename);
bool is_in_target_list(struct target_list * list, const char * nodename);
void target_list_remove(struct target_list * list, const char * nodename);
/*-----------------------------------------------------*/
#endif
目标.c
#include "target.h"
/*----------------------------------------------------------*/
//This function will initialize a new target_list with name targetname
//This function will assume that target_list is already allocated
void target_list_init(struct target_list * list, const char * targetname){
verify(list != NULL, "null arg list");
verify(targetname != NULL, "null arg targetname");
verify(targetname[0] != ' ',"empty arg targetname");
list->name = Strdup(targetname);
list->head = list->tail = NULL;
}
/*----------------------------------------------------------*/
//This function will allocate a new target_list and return a pointer to it
struct target_list * target_list_alloc(const char * targetname){
verify(targetname != NULL, "null arg targetname");
verify(targetname[0] != ' ',"empty arg targetname");
struct target_list * list = malloc(sizeof(struct target_list));
list->name = Strdup(targetname);
list->head = list->tail = NULL;
return list;
}
/*---------------------------------------------------------*/
//This function will deallocate a target_list
void target_list_deallocate(struct target_list * list){
verify(list != NULL,"null arg list");
free(list->name);
struct target_node * prev = NULL;
for(struct target_node * p = list->head; p != NULL; p= p->next){
free(prev);
free(p->name);
prev = p;
}
free(prev);
free(list);
}
/*----------------------------------------------------------*/
//This function will print a target_list
void target_list_print(struct target_list * list){
verify(list != NULL, "null arg list");
printf("list of targets: %sn",safe_string(list->name));
if(list->head == NULL){
printf(" <empty>n");
}
else{
for(struct target_node * p = list->head; p != NULL; p = p->next){
printf(" %sn",p->name);
}
}
}
/*-----------------------------------------------------------*/
//This function will append a new target_node onto target_list at the end of it
void target_list_append(struct target_list * list, const char * nodename){
verify(list != NULL, "null arg list");
verify(nodename != NULL, "null arg nodename");
verify(nodename[0] != ' ', "empty arg nodename");
struct target_node * new_node = malloc(sizeof(struct target_node));
new_node->next = NULL;
new_node->name = Strdup(nodename);
new_node->src_list = NULL;
new_node->rec_list = NULL;
if(list->head == NULL){
list->head = list->tail = new_node;
}
else{
list->tail->next = new_node;
list->tail = new_node;
}
}
/*--------------------------------------------------------*/
//This function returns 1 if the nodename is already in the target_list and 0 if not
bool is_in_target_list(struct target_list * list, const char * nodename){
verify(list != NULL, "null arg list");
verify(nodename != NULL, "null arg nodename");
verify(nodename[0] != ' ', "empty arg nodename");
for(struct target_node * p = list->head; p != NULL; p = p->next){
if(strcmp(nodename,p->name) == 0){
return 1;
}
}
return 0;
}
/*------------------------------------------------------*/
//This function removes a node with name nodename from target_list */
void target_list_remove(struct target_list * list, const char * nodename){
verify(list != NULL, "null arg list");
verify(nodename != NULL, "null arg nodename");
verify(nodename[0] != ' ', "empty arg nodename");
if(is_in_target_list(list,nodename)){
struct target_node * prev = NULL;
struct target_node * cur = list->head;
while(cur != NULL){
if(strcmp(cur->name,nodename) == 0){
break;
}
prev = cur;
cur = cur->next;
}
//case 1: removing head pointer
if(cur == list->head){
free(cur->name);
free(cur->src_list);
free(cur->rec_list);
free(cur);
list->head = NULL;
list->tail = NULL;
free(prev);
cur = NULL;
prev = NULL;
}
//case 2: removing tail pointer
else if(cur == list->tail){
free(cur->name);
free(cur->src_list);
free(cur->rec_list);
free(cur);
list->tail = prev;
free(prev);
prev = NULL;
cur = NULL;
}
//case 3: removing a middle node
else{
prev->next = cur->next;
free(cur->name);
free(cur->src_list);
free(cur->rec_list);
free(cur);
cur = NULL;
free(prev);
prev = NULL;
}
}
else{
fprintf(stderr,"%s: Error %s is not in %s, cannot remove it from %sn",prog,nodename,list->name,list->name);
}
}
/*----------------------------------------------------*/
在其他位置定义了几个辅助函数（验证,..），但它们不会影响malloc
编译：
gcc -Wall -Wextra -std=c99 -g -o test driver.c target.c cmpsc311.c
driver.c:5: warning: unused parameter ‘argc’
driver.c:5: warning: unused parameter ‘argv’
输出：
list of targets: list
<empty>
list of targets: list
G
B
list of targets: list
G
B
S
list of targets: list
G
S
[no name]: Error Bl is not in list, cannot remove it from list
[no name]: Error Br is not in list, cannot remove it from list
list of targets: list
G
S
list of targets: list
Ba
运行 gdb 并查看列表后，列表>头，列表>尾和new_node （Ba） 我不知道为什么new_node在 malloc ed 时会得到列表>头的地址
分行：
78 struct target_node * new_node = malloc(sizeof(struct target_node));
4: new_node = (struct target_node *) 0x3a00000000
3: list->tail = (struct target_node *) 0x100100940
2: list->head = (struct target_node *) 0x1001008e0
1: list = (struct target_list *) 0x1001008b0
(gdb) n
79 new_node->next = NULL;
4: new_node = (struct target_node *) 0x1001008e0
3: list->tail = (struct target_node *) 0x100100940
2: list->head = (struct target_node *) 0x1001008e0
1: list = (struct target_list *) 0x1001008b0
(gdb) n
谁能告诉我为什么会这样以及如何解决它？谢谢
您的target_list_remove()函数看起来很假。遍历列表后，prev指向要删除的元素（prev = cur;），cur指向下一个元素，而prev应指向要删除的元素之前的元素。
另外，您正在cur和prev上调用free()，但我的猜测是您只想删除一个元素。
修复指针并仅调用free()一次。
问题出在您的删除函数中。您正在呼叫free(prev)因此在呼叫target_list_remove(target,"B");中，列表的负责人也被释放。然后，分配器将重新使用存储，以便下次调用 malloc 。您可以使用诸如valgrind之类的工具来调试这样的内存问题。
当你在target_list_remove中删除"B"时，它会下降到"case 3: removing a middle node"，因为你的列表在这一点上看起来像这样：
G -> B -> S
在该段代码中，您将从列表中删除 cur 节点 （ prev->next = cur->next ），并继续释放当前节点的资源。此时，您的列表如下所示：
G -> S
。但是在释放 cur 节点后，您继续释放 prev 节点（即列表头）并将其设置为 null。
当附加"Ba"节点时，当它遇到条件时list->head == NULL它是真的，因此将列表的头部和尾部设置为新的"Ba"节点。