链接列表添加功能不按预期工作

Question

我正在学习C中的数据结构，并认为实现相同， 下面是代码和它给怪异的输出，它显示正确的数据时，显示在添加记录功能，但当相同函数被调用从主值改变，我知道它与价值调用有关，但无法弄清楚确切的原因。

PS：抱歉，如果程序过长或不按标准

#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显示正确的，但同样从主叫值改变

附加功能后，当

Answer 1

问题是传递给add_record的record是main中的record的副本。当参数是一个结构时，这就是通过值传递的方式。所以对record的更改只会影响副本，而不会影响原始副本。

要解决此问题，声明record为指针

void add_record(data_record *list,data_record *record,int position) 
{ 
    ... 

    list_pointer->next_record = record; 
    record->next_record = next_record; 

    ... 
} 

和main

add_record(start,&record,2); 

---

旁注通过记录的地址：这是毫无意义的start传递给generate_link_list由于start不包含generate_link_list需要的任何信息或使用。因此，将其更改为：

data_record *generate_link_list(int array_length) 
{ 
    data_record *list = get_record(); 

    ... 
} 

---

另注：正如评论所指出的@JonathanLeffler，你应该总是使用get_record函数来创建记录。我会走得更远，并说get_record和initialize_record应该组合成单一功能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; 
    } 
} 

然后在main代码变得

// 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); 

通过使用列表中的create_record所有的记录，你可以放心地在需要的时候free在列表中的项目。