help error writing to file

Hi!

I'm trying to code a program that needs to store data in a binary file.
I already did the first try of the code and it works fine except when the file hasn't been created yet and I try to read. I thought that the fopen fuction would just return NULL in this case.

My code to read is:

Code:

int leLista(char* nome)
{
	FILE *ficheiro = fopen(nome, "rb");
	int cnt = -1;
	Restaurante* auxiliar;

	if (ficheiro != NULL)
	{
		do{
			auxiliar = (Restaurante*)malloc(sizeof(Restaurante));
			cnt = fread(auxiliar, sizeof(Restaurante), 1, ficheiro);
			printf("batatas %s\n", auxiliar->nome);
			if (cnt == 1)
			{
				inserir(criaNo(auxiliar));
			}
		}while(cnt != 0);

		imprimeLista();
	}


	int valor = fclose(ficheiro);
	
	return cnt;
}

It generates a segmentation fault. If I run it in gdb I get

Code:

Program received signal SIGSEGV, Segmentation fault.
0xb7eb25dd in fclose () from /lib/tls/i686/cmov/libc.so.6
(gdb) print errno
Cannot find thread-local variables on this target

What am doing wrong?

Thanks in advance

I am guessing Restaurante is a struct of sorts that you've written to a binary file. Well, this isn't going to work. You can't simply read auxiliar->nome the same way you wrote it. What is written into the file is the address stored in nome, not the contents of nome. When you read it back, you'll be reading an address that you may or may not have access to. This means nome points to some unknown location when you run the program again.

The solution is to write your own functions to write and read structs of Restaurante yourself, preferably in text form, to keep it all portable and easy on yourself.

I would put the fclose inside your ( != NULL) conditional also, otherwise your application may end up tryng to close a NULL pointer (which several OS's don't like you doing).

Thanks trillianjedi I'll try to do that.

In the meanwhile, MacGyver you said

I am guessing Restaurante is a struct of sorts that you've written to a binary file. Well, this isn't going to work. You can't simply read auxiliar->nome the same way you wrote it. What is written into the file is the address stored in nome, not the contents of nome. When you read it back, you'll be reading an address that you may or may not have access to. This means nome points to some unknown location when you run the program again.

I don't understand, when I try to open the binary file in text editor, most of it isn't understandable but the name is there I can read it. Maybe I understood you wrong?
Also I need to use binary files, it's part of the assignment

Thanks so much trillianjedi it works fine (so far ^_^ )

Well, if it's part of the assignment then whatever. If you're reading and writing during the same session, you should be ok, but many times files are used after a process has shut down and is started back up again, in which case the pointers are useless.