Thread: Help with linked list

Hi!

I have problem with the "ReadList" and "WriteList" function.

Code:

# include <stdio.h>
# include <stdlib.h>
# include <ctype.h>
# include <conio.h>

# define FALSE 0

typedef struct 
{  
	int Value;
	struct List *link;
} List;

// other functions
void clrscr (void);
void Menu (int *Choose);
// functions for the list
List *AddElement (List *start, int Data);
void ReadList (List *start, char File01[]);
void WriteList (List *start, char File01[]);
void PrintList (List *start);

int main()
{
	int Choose, Data;
	List *start = NULL;
               
	start = ReadList(start, "data.txt");
	do
	{
		Menu(&Choose);
		switch (Choose)
		{
			case 1:
				printf("\nEnter number: ");
				scanf("%d", &Data);
				start = AddElement(start, Data); 
				break;
			case 2:
				if (start != NULL)
				{
					PrintList(start);
				}
				else
				{
					printf("\nList is empty.");
				}
				getch();
				break;
			case 3:
				break;
			default:
				printf("\nWrong selection. Try again.");
				getch();
				break;
		}
	} while (Choose != 3);
                WriteList (start, "data.txt");
	return 0;	
}

void Menu (int *Choose) 
{
    unsigned char Char;

    do 
	{
		clrscr();
		printf("List");
		printf("\n\n1 - Add element into sorted list");
		printf("\n2 - Print elements on the screen");
		printf("\n3 - Exit");
		printf("\n\nChoose: ");
		Char = getchar();
		if ((isdigit (Char) == FALSE) && (Char != '\n')) 
		{
			printf ("\nYou must enter number."); getch();
		}
    } while (isdigit (Char) == FALSE);
    *Choose = (int) Char - '0'; 
}

void clrscr()
{
	system("cls");
}

List *AddElement (List *start, int Data)
{
	List *pom, *New;
	
	New = (List *) malloc(sizeof(List));
	New->Value = Data;
	if ( (start == NULL) || (New->Value <= start->Value) ) 
	{
		(List *)New->link = start;
		start = New;
	}
	else
	{
		pom = start;	
		while ( (pom->link != NULL) && (New->Value > ((List *)pom->link)->Value) )
		{
			pom = (List *)pom->link;
		}
		New->link = pom->link;
		(List *)pom->link = New;
		
	}
	return start;
}

void PrintList (List *start)
{
	while (start != NULL)
	{
		printf("%d\t", start->Value);
		start = (List *)start->link;
	}
}

Thnx in advance .

Uf, I totally forgot to copy/paste these two functions:

Code:

List *ReadList (List *start, char File01[])
{
	FILE *fin;
	List *New;

	fin = fopen(File01, "rb");
	while ( !feof(fin) )
	{
		New = (List *) malloc (sizeof(List));
		fread(New, sizeof(List), 1, fin);
		(List *)New->link = start;
		start = New;
	}
	fclose(fin);
	return start;
}

void WriteList (List *start, char File01[])
{
	FILE *fout;

	fout = fopen(File01, "wb+");
	while (start != NULL)
	{
		fwrite(start, sizeof(List), 1, fout);
		start = (List *)start->link;
	}
	fclose(fout);
}

The problem is that when I exit my program, the WriteList function always adds 0 to the "data.txt" file. What is wrong?

typedef struct
{
int Value;
struct List *link;
} List;

The 0 is the value of link for the last element.... the value after the last element is NULL, and NULL is 0. So... the last value in your data.txt is going to be 0.

But why the program doesn't print out the 0 on the screen when I use function "PrintList"?

Yes I used file pointers before and this code is right. I have a string and a pointer to that string (File01[100] and *File01Ptr). In my case a file pointer is "fin" and "fout".

If I write "printf("%s", File01Ptr);" I get "data.txt" which is totally right.

If you write linked lists in your sleep than, please, help me out and tell me why do I get those 0 in my file.

Ok I changed the code.

Here's the file and change it's extension to .txt.

Code:

void OpenFile(FILE **fptr, char path[], char mode[]);

int main()
{
	int Choose, Data;
	List *start = NULL;
	FILE *fin;

	OpenFile(&fin,"data.txt","rb");

	int count = 0;
	while ( !feof(fin))
	{
		start = ReadList(fin,start);
		count ++;
	}
	//...
	return 0;
}

void OpenFile(FILE **fptr, char path[], char mode[])
{
	*fptr = fopen(path,mode);
	if (*fptr == NULL) 
	{
		fprintf(stderr,"Error: File a:\\name?? is missing!\n");
		exit(1);
	}
}

This is cleaner. Okay now for the ReadList function.