Thread: load file to structure

Hello, I am working on function that builds the linked list of nodes, program exits when it comes to the line where file needs to be opened. don't understand why? To the function I am passing pointer to the new list and a file name. I was trying to find the answere myself.....with no success

I also have another question, when I am passing linked list to the function and when I need to loop through it or somthing else.....does it always start from a first node ...head or I need to tell the function from where in a linked list to sart to do whatever .....if yes, can I do it like k=NULL, and then k=k->next?


thank you in advance

Code:

#include<stdio.h>
#include"keytype.h"

void load(KEYS k,char *fn)
{
	FILE* fp;
	k=(KEYS*)malloc(sizeof(KEYS));
	
	if((fp=fopen(fn, "r"))== NULL)
	{
		printf("Error, the file does not exist");
		exit(1);
	}

	if(ftell(fp)==NULL)
		exit(2);
	
	fscanf(fp, "%s", k->addressee);
	fscanf(fp, "%s", k->sender);
	fscanf(fp, "%s", k->regarding);
	fscanf(fp, "%d%*c%d%*c%d", &k->date.month, &k->date.day, &k->date.year);
	fscanf(fp, "%d", &k->id);
	fscanf(fp, "%s", k->fname);

	while(!feof(fp))
	{	
		k->next=(KEYS*)malloc(sizeof(KEYS));
		k=k->next;
		
		fscanf(fp, "%s", k->next->addressee);
		fscanf(fp, "%s", k->next->sender);
		fscanf(fp, "%s", k->next->regarding);
		fscanf(fp, "%d%*c%d%*c%d", &k->next->date.month, &k->next->date.day, &k->next->date.year);
		fscanf(fp, "%d", &k->next->id);
		fscanf(fp, "%s", k->next->fname);
	}
	fclose(fp);


	
	while(k->next!=NULL)
	{
		k=k->next;
		printf("%s %s %d\n", k->next->addressee, k->next->sender, k->next->id);

	}
}

Thank you.

This is the cast (in red):

Code:

k=(KEYS*)malloc(sizeof(KEYS));

Casts are sometimes needed in C, but never for the return value of malloc(). <<== Eh, maybe not, see note in blue

With the cast, most compilers will not give you the error that you do not have the right include file (stdlib.h), in place.

I'm going to retract what I said about casting, in this case. You don't need to do any casting of malloc()'s result for a *standard* data type, but for a struct, you may need to cast. -- Sorry for the confusion, but I'm not familiar with casts made from malloc's pointer, to struct's.


It would be a good idea to test the return value of malloc(), and ensure that it has done it's job, correctly.

When you step through the program, you should see exactly what line of code it's failing on. The question is not if fn is a constant char *, but is fn a constant char * to a *file*.

Have you checked that file with an editor to see if it can be read?

Originally Posted by Adak

I'm going to retract what I said about casting, in this case. You don't need to do any casting of malloc()'s result for a *standard* data type, but for a struct, you may need to cast. -- Sorry for the confusion, but I'm not familiar with casts made from malloc's pointer, to struct's.

Actually, your original assertion was correct: in C, a pointer to void is implicitly convertible to a pointer to any other pointer to an object type. As such, the return value of malloc need not be cast to be converted to a pointer to a struct type.

That's because you are using a C++ compiler, not a C compiler. Rename that file from test.cpp to test.c and see what happens...

Originally Posted by nonoob

Once and for all, malarkey!

That implies that you are compiling as C++, not as C. If you need to be compatible with C++, then go ahead and use that cast.

Originally Posted by nonoob

I can't test it out because renaming test.cpp to test.c means I break everything. If I double click 'test.c', the Visual Studio opens to show me the file, but there is no green arrow (it's grey) to compile/build.

It might be because test.c is not included in the project, though that should not be the case if you rename using the IDE. Anyway, you can force compilation as C even with a .cpp file extension. Go to Project -> Properties -> Configuration Properties -> C/C++ -> Advanced. In the "Compile As" field, select "Compile as C Code (/TC)".