Malloc printf with strange characters....

[Gil Carvalho]

Hi (again)

Hope this is my last post asking some help...

I have a function to see my registered players but i must use malloc

int listarTop()
{
    struct jogador *j;
    int retorno, cont = 0;
	FILE *f;
	if ((f= fopen("registos.dat", "rb")) == NULL)
	{
		printf("Erro ao abrir ficheiro\n");
	}
	else
	{
	    j=(struct jogador *)malloc(sizeof(struct jogador));
	    if (j==NULL)
		{
			printf("Erro na alocacao de memoria!");
			exit (1);
		}
	    printf("\nNome: %s",j->nome);
		printf("\nNickname : %s",j->nick);
		printf("\nPassword : %s",j->pass);
		printf("\nLog : %d",j->log);
		printf("\n");
	}
	free(j);
	fclose(f);
	return 0;
}

my struct is
char nome[100];
char nick[100];
char pass[100];
int log;


Well, i have no errors but the prints are strange characters

What's wrong?

[laserlight]

The problem is that you immediately try to print j->nome, etc, after using malloc. You did not assign anything, so you get junk.

[Gil Carvalho]

I think it's not necessary to use malloc since the assisgment don't specify it's must be.

So i use a regular fread file

int listarTop(struct jogador *j)
{
    int retorno, cont = 0;
	FILE *f;
	if ((f= fopen("registos.dat", "rb")) == NULL)
	{
		printf("Erro ao abrir ficheiro\n");
	}
	printf ("\n*=============================================================================*\n");
    printf ("|                       >>>>Visualizacao de perguntas<<<<                      |\n");
    printf ("*=============================================================================*\n");
    printf ("                                                                               \n");
	retorno = fread(j, sizeof *j, 1, f);
	while ( retorno == 1)
	{
		cont++;
		printf("\nNome: %s",j->nome);
		printf("\nNickname: %s",j->nick);
		printf("\nPassword: %s",j->pass);
		printf("\nLog : %d",j->log);
		printf("\n");
		retorno= fread(j, sizeof *j, 1, f);
	}
	printf(" \n\n %d perguntas registadas \n", cont);
	printf ("*=============================================================================*\n");
	fclose(f);
}

But i have a seg fault here.

retorno = fread(j, sizeof *j, 1, f);

The file exist since the error is after, and i use a function login where i put my user and pass and i can access.

[christop]

How is listarTop called? Are you passing a valid pointer to a struct jogador? Post the code that calls listarTop.

Also, your loop reads all data from the file into a single structure, so you will end up with only the last data that is read from the file.

[AndiPersti]

FILE *f;
if ((f= fopen("registos.dat", "rb")) == NULL)
{
    printf("Erro ao abrir ficheiro\n");
}
... rest of your code

You check if fopen() was succesful (which is good) but you only print an error message and then continue with the program. So this check is rather useless.

The file exist since the error is after, and i use a function login where i put my user and pass and i can access.

As you try to read from the file regardless if fopen() was succesful or not, you can't be sure, that f is a valid file pointer

BTW: You declare listarTop() as returning an int, but you never return anything.

Bye, Andreas

[Gil Carvalho]

Hi

The listarTop is called like this

listarTop(&j)

I just found out what was the problem, AndiPersti you gonna kill me with all reasons, arguments where in different order.
I'm so stupid...

Now, i can read the file, everything is ok but i have those fields

name
nickname
pass
log

If after a game i just want to update the log field, i just have to write

fwrite(&log, sizeof *j, 1,f)

Thanks people