Code:
(gdb) run
Starting program: a.out
Breakpoint 1, add_day_node (calender=0x7fffffffde40) at foo.c:94
94 calender->current_day = tmp_node;
(gdb) p tmp_node
$1 = (Days_Node *) 0x603010
(gdb) p *tmp_node
$2 = {day_num = 1, weekday = 0x603030 "Monday", next = 0x603010}
(gdb) c
Continuing.
Breakpoint 1, add_day_node (calender=0x7fffffffde40) at foo.c:94
94 calender->current_day = tmp_node;
(gdb) p tmp_node
$3 = (Days_Node *) 0x603050
(gdb) p *tmp_node
$4 = {day_num = 2, weekday = 0x603070 "Tuesday", next = 0x603050}
(gdb) c
Continuing.
Breakpoint 1, add_day_node (calender=0x7fffffffde40) at foo.c:94
94 calender->current_day = tmp_node;
(gdb) p tmp_node
$5 = (Days_Node *) 0x603090
(gdb) p *tmp_node
$6 = {day_num = 3, weekday = 0x6030b0 "Wendnesday", next = 0x603090}
Every node points to itself.
If you're not drawing diagrams like this, then start doing so.
It will help you figure out what needs to be assigned, and in what order.
Here is some new code for you to study.
Code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
enum DAY {MON = 1, TUES, WED, THURS, FRI, SAT, SUN};
enum MONTH {JAN = 1, FEB, MARCH, JUNE, JULY, AUG, SEPT, OCT, NOV, DEC};
typedef struct Days_Node
{
int day_num;
char *weekday;
struct Days_Node *next;
}Days_Node;
typedef struct Months_Node
{
int month_num;
char *month;
struct Months_Node *next;
}Months_Node;
typedef struct Lists
{
struct Days_Node *current_day;
struct Months_Node *current_month;
}Lists;
struct Days_Node *debugDays[100];
int ndebugDays = 0;
Days_Node *get_day_memory(void);
Months_Node *get_month_memory(void);
char *get_string_memory(int x);
void add_day_node(Lists *calender);
void set_day_data(Days_Node *node, int x);
void add_month_node(Lists *calender);
void free_list(Lists *calender);
int main()
{
int i;
Lists calender;
calender.current_day = NULL;
calender.current_month = NULL;
add_day_node(&calender);
for ( i = 0 ; i < ndebugDays ; i++ ) {
printf("self=%p next=%p\n", debugDays[i], debugDays[i]->next);
}
while (calender.current_day->day_num != MON)
{
calender.current_day = calender.current_day->next;
}
for (i = 1; i < 5; i++)
{
printf("day of the week is %s\n", calender.current_day->weekday);
calender.current_day = calender.current_day->next;
if (calender.current_day->next == NULL)
{
printf("not circular\n");
}
}
free_list(&calender);
return 0;
}
Days_Node *get_day_memory(void)
{
Days_Node *result = malloc(sizeof(Days_Node));
debugDays[ndebugDays++] = result;
return result;
}
Months_Node *get_month_memory(void)
{
return malloc(sizeof(Months_Node));
}
char *get_string_memory(int x)
{
return (char *)malloc(x + 1);
}
void adder(Lists *calender, Days_Node *node)
{
if ( calender->current_day == NULL )
{
// empty
calender->current_day = node;
node->next = node;
}
else
{
// more than one node
node->next = calender->current_day->next; // A
calender->current_day->next = node; // B
calender->current_day = node; // C
}
}
void add_day_node(Lists *calender)
{
int i;
for (i = 1; i < 4; i++)
{
Days_Node *tmp_node = get_day_memory();
set_day_data(tmp_node, i);
tmp_node->next = NULL;
adder(calender, tmp_node);
}
}
void set_day_data(Days_Node *node, int x)
{
char *days[] = {"", "Monday", "Tuesday", "Wendnesday", "Thursday", "Friday", "Saturday", "Sunday"};
if (!node)
{
fprintf(stderr, "unable to allocate memory");
exit(EXIT_FAILURE);
}
node->day_num = x;
node->weekday = get_string_memory(strlen(days[x]));
strcpy(node->weekday, days[x]);
}
void add_month_node(Lists *calender);
void free_list(Lists *calender)
{
Days_Node *tmp_node = calender->current_day->next;
calender->current_day->next = NULL;
calender->current_day = tmp_node;
while(calender->current_day->next)
{
tmp_node = calender->current_day->next;
free(calender->current_day->weekday);
free(calender->current_day);
calender->current_day = tmp_node;
printf("freed memory\n");
}
}
Key points.
1. The adder does exactly ONE thing, and one thing only! You need to stop trying to do too much in each function.
2. The ABC comments in the code of adder() relate to the picture.
3. Don't be afraid to add debug code such as the debugDays. You can do anything you like if you think it will add clarity or insight into what is going on.
Code:
$ ./a.out
self=0x1615010 next=0x1615050
self=0x1615050 next=0x1615090
self=0x1615090 next=0x1615010
day of the week is Monday
day of the week is Tuesday
day of the week is Wendnesday
day of the week is Monday
freed memory
freed memory
You can see in the debug each .next does point to the next self, and the last one points back to the start.
I'll leave you to fix your free loop.
