Thread: Binary File I/O Problem

your idea about your sizeof() in the fread() being wrong is correct. think; what variable types are new->msg and *(new->msg)?

Code:

items_read = fread(new->msg,sizeof(new->msg),1,fp);

You are reading in 1 item of the size of a pointer (may be different from the size of an int?). You need to read in length items of whatever your int size happens to be. I believe you want:

Code:

items_read = fread(new->msg,sizeof(int),new->length,fp);

Hmm damn, this thing is cursing me.. that doesn't work either it should but it doesn't - argh don't want to put in all of my code because its kinda too long.
Im totally confused..

Ok, heres a bit of my code just to clarify a bit: it looks slightly different to the example I put above but I didn't think it would really matter:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <time.h>
#include <ctype.h>
#include "codeops.c"

struct message {
    time_t time;
    char location[24];
    int device_id;
    double frequency;
    int burst_size;
    int msg_len;
};    

struct node {
    struct message data;
    int* msg;
    struct node* next;
};

int main(int argc, char **argv)
{
    int i = 1, items_read = 0,j = 0;
    struct node *empty = NULL;
    struct node *new = (struct node*)malloc(sizeof(struct node)); 
    /* Check for arguments if argc == 1 display usage */
    if (argc == 1){
        printf("usage: codebreak messagefile\n");
        printf("where: messagefile contains intercepts in the correct binary format\n");
        return 0;
    }
	FILE *fp; 

	while (i < argc){
	fp = fopen(argv[i],"rb");
	i++; 

	items_read = fread(new,(sizeof(new->data)),1,fp);
	if (items_read != 1)
		break;
	new->msg = malloc(sizeof(int)*(new->data.msg_len+1));
	items_read = fread(new->msg,sizeof(int),new->data.msg_len,fp);

	printf("Msg_len: %d\n",new->data.msg_len); // debugging printf()
	
	printf("%s",new->msg);	 // debugging printf()
	sorted_insert(&empty,new);
	}        
    print_list(empty);
    free_list(&empty);
    return 0;
}

The functions sorted_insert(), print_list() and free_list() does as the name suggested.

Code:

#include "codeops.c"

You really should not be including c source files. If your project is a multi-file project then compile/link it as such.

Also, are you positive that your code that writes the file is working properly? Could we also see that code?

Code:

	items_read = fread(new->msg,sizeof(int),new->data.msg_len,fp);

	printf("Msg_len: %d\n",new->data.msg_len); // debugging printf()

As an additional debug check, you can also print out the return value of the fread, i.e. items_read and see if that goes along with what you are expecting.

Code:

printf("%s",new->msg);	 // debugging printf()

What do you expect this to do? msg is an int pointer and you are telling printf to expect a character string.

If there is not too much data to read into your list, you can try printing out the list as each successive record is read from the file and inserted into the list. This may necessitate temporarily changing the print routine so that it pauses after displaying each node of the list to allow you to debug better.

I'm not sure if you wanted me to post the code on the print_list() and sorted_insert() hk_mp5kpdw, but here they are anyway:

Code:

void print_list(struct node* root)
{
        if (root == NULL){
            printf("Nothing to print! Empty list!\n");
            return;
        }    
        struct node* current = root;
        while (current != NULL){
            printf("%s %s/%d %s\n",timestamp((current->data).time),
            (current->data).location, (current->data).device_id,
            (current->msg));
            
            current = current->next;
        }
}  

void sorted_insert(struct node **headRef, struct node *newNode)
{
	struct node** currentRef = headRef;
	
	/* traverse the tree */
	while (*currentRef != NULL && (int)((*currentRef)->data.time) > (int)(newNode->data.time))
	currentRef = &((*currentRef)->next);

	/* insert here */
	newNode->next = *currentRef;
	*currentRef = newNode;
}

Ok, I have NO idea whats going on but I just used a for loop to print each new->msg[j] element and it works, I tried it last nite but it didn't work.. argh its toying with me

Originally Posted by Orion

Ok, I have NO idea whats going on but I just used a for loop to print each new->msg[j] element and it works, I tried it last nite but it didn't work..

Originally Posted by Orion

About the printing the int pointer as a string - it was in the specifications of the assignment so I have to use it like that. I tried using a for loop to control and print each int element (into char) to no success as well.

It did or it didn't work?

You may need to post your complete source code and the input file zipped up as an attachment. Looks almost like the msg field is supposed to point to a bunch of character data and not integers. Maybe also include as much as you can about the "specification".

I should of made myself more clear, it works now
The specification just said:

msg: The message content is a sequence of msg_len integers. type: int[]

I'm not sure why its int instead of char, but I read somewhere that for binary files (or text files in general) an integer is favoured over a character since you can determine the EOF without conflicting with one of the binary values for a particular character. Which is probably why EOF is sometimes -1, since there is no character for -1 in the character set, but then again I could be purely wrong