我当时正在学习C语言中的数据结构,并想实现它,
下面是代码及其给出的奇怪输出,在添加记录函数中显示时显示正确的数据,但是当从main调用同一函数时,值已更改,我知道其与按值调用有关,但无法弄清楚确切的数据原因。
PS:很抱歉,如果程序太长或不符合标准
#include <stdio.h>
#include <stdlib.h>
struct record;
typedef struct record data_record;
struct record{
int data;
struct record *next_record;
};
// forward function declarations
data_record *get_record();
void initialize_record(data_record *,int);
void display_record(data_record *);
void display_list(data_record *,int);
data_record *generate_link_list(data_record *,int);
void add_record(data_record *,data_record,int);
int main(int argc,char *argv[])
{
printf("Initializing the data ... \n");
printf("Data length: %d \n",sizeof(data_record));
int array_length = 5;
data_record *start;
// generate_list function
start = generate_link_list(start,array_length);
printf("------------------------------------\n\n");
display_list(start,array_length);
printf("Address : %x \n",start);
// add the extra item to the existing list
data_record record;
record.data = 100;
record.next_record = NULL;
add_record(start,record,2);
display_list(start,array_length +1);
printf("Terminating the program \n");
return 0;
}
data_record *get_record()
{
return (data_record *)malloc(sizeof(data_record));
}
void initialize_record(data_record *record,int data)
{
record->data = data;
record->next_record = NULL;
}
void display_record(data_record *record)
{
printf("Printing data: \t");
printf("Data: %d \t",record->data);
printf("Next Item address: %x \n",record->next_record);
}
void display_list(data_record *list,int length)
{
data_record *list_pointer = list;
printf("Printing the list: \n");
int index;
for(index = 0;index < length;index++)
{
display_record(list_pointer);
list_pointer = list_pointer->next_record;
}
printf("Done with the printing \n");
}
data_record *generate_link_list(data_record *list,int array_length)
{
list = get_record();
initialize_record(list,0);
data_record *current_record_pointer, *record;
int index = 0;
current_record_pointer = list;
printf("First record: ");
display_record(current_record_pointer);
for(index = 1;index < array_length;index ++)
{
record = get_record();
initialize_record(record,index);
current_record_pointer->next_record = record;
current_record_pointer = record;
}
return list;
}
void add_record(data_record *list,data_record record,int position)
{
printf("Start address %x \n",list);
printf("New record address %x \n",&record);
data_record *list_pointer = list;
int list_position = 0;
for(list_position = 0;list_position < position - 1;list_position ++)
{
list_pointer = list_pointer->next_record;
}
if(list_pointer != NULL)
{
data_record *next_record = list_pointer->next_record;
list_pointer->next_record = &record;
record.next_record = next_record;
}
display_list(list,6);
}
从add函数调用时,display_list显示正确,但是在add函数更改后从main调用时,display_list正确
最佳答案
问题是传递给record
的add_record
是record
中main
的副本。当参数是结构时,值传递就是这样工作的。因此,对record
所做的更改只会影响副本,而不会影响原始副本。
要解决此问题,请声明record
作为指针
void add_record(data_record *list,data_record *record,int position)
{
...
list_pointer->next_record = record;
record->next_record = next_record;
...
}
并在
main
中传递记录的地址add_record(start,&record,2);
注意:将
start
传递给generate_link_list
是没有意义的,因为start
不包含generate_link_list
所需或使用的任何信息。因此将其更改为:data_record *generate_link_list(int array_length)
{
data_record *list = get_record();
...
}
另一个说明:正如@JonathanLeffler在评论中指出的那样,您应该始终使用
get_record
函数创建记录。我会更进一步地说get_record
和initialize_record
应该合并为单个函数create_record
,例如data_record *create_record(int data)
{
data_record *record = malloc(sizeof(data_record));
if ( record )
{
record->data = data;
record->next_record = NULL;
}
}
然后
main
中的代码变为// add the extra item to the existing list
data_record *record = create_record(100);
if (record)
add_record(start,record,2);
display_list(start,array_length +1);
通过对列表中的所有记录使用
create_record
,可以在需要时安全地free
列表中的项目。关于c - 链接列表添加功能无法正常工作,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/38413836/