C Programming - File - fwrite - c

Question

I've got a question regarding programming and files.
while(current!=NULL)
{
if(current->Id_Doctor!='\0')
{
current=current->next;
id_doc=(current->Id_Doctor);
}
if(current->Id_Doctor=='\0')
{
id_doc=id_doc+1;
printf("%d", id_doc);
break;
}
}
fwrite(&id_doc, sizeof(char), 1, Archivo);
I dont know why but it aint writing the value of id_doc on the binary file called 'Archivo'...what could be the problem?
I added a printf of id_doc and the value was printed..I really dont know
Ok, heres the full code(more-less):
struct Medico
{
int Id_Doctor;
int Estado;
char Nombre[60];
char Clave_Acceso[20];
char Especialidad[40];
struct Medico *next;
};
void Dar_Alta_Med (int estado);
void MenuPrincipal(char enta);
int main(void)
{
char enta;
MenuPrincipal(enta);
}
void Dar_Alta_Med(int estado)
{
struct Medico * head = NULL;
struct Medico * prev, *current;
char nombre_doc[60], especialida[40], password[20];
int id_doc=0, estado_doc=1;
FILE *Archivo;
const char *md1="\n<md>\n";
const char *id_doc1="<id_doctor> ";
Archivo=fopen("md.dat", "ab+");
fwrite(md1, 1, strlen(md1), Archivo);
fwrite(id_doc1, 1, strlen(id_doc1), Archivo);
current = (struct Medico *) malloc (sizeof(struct Medico));
current->Id_Doctor=id_doc;
while(current!=NULL)
{
if(current->Id_Doctor!='\0')
{
current=current->next;
id_doc=(current->Id_Doctor);
}
else
{
id_doc=id_doc+1;
printf("%d", id_doc);
break;
}
}
fwrite(&id_doc, sizeof(id_doc), 1, Archivo);
printf("Ingresa el nombre del Doctor a dar de alta: ");
fclose(Archivo);
}
Im dying here, please help :/

Answer 1

Try adding fflush(Archivo); to force a write of all buffered data.
Also, this statement: if(current->Id_Doctor=='\0') really ought to be an else since there is no other thing it can be but '\0'

Answer 2

Three things:
Make sure your fopen is successful.
Archivo=fopen("md.dat", "ab+");
if (Archivo == NULL)
{
perror("Failed to open file Archivo");
...
}
Make sure you are checking the success of your fwrite's.
if (fwrite(&id_doc, sizeof(id_doc), 1, Archivo) < 1)
{
perror("Failed to write to file Archivo");
...
}
Make sure you have a fclose to close the file properly.
if (fclose(Archivo) != 0)
{
perror("Failed to close file Archivo");
...
}
Now that you've post a full sample of your code I guess I should ask if error checking is just left out for brevity? If not, you should think about adding it.
If you're expecting the value of id_doc to be in display format in the output file you'll have to convert the int to a string (using snprintf or similar) and write the string to the output file instead.

Answer 3

fwrite(&id_doc, sizeof(char), 1, Archivo);
If you defined id_doc as anything other than a char it will write \0 to the file.
Much cleaner would be:
fwrite(&id_doc, sizeof(id_doc), 1, Archivo);

Answer 4

If your first current is an Id_Doctor you have an endless loop.
If there is no current after your last current that is not an Id_Doctor, you get an illegal pointer derefenciation.
For your Problem:
try the flush() family.

Answer 5

You're passing a pointer to a FOUR-BYTE INT, but only writing ONE BYTE (the wrong byte)!
Solution: declare id_doc as "char", not "int".

Answer 6

You have previously written the strings "\n<md>\n" and"<id_doctor> " to the file Archivo, which seems to indicate that it is not a binary file at all, but rather an XML-style file.
In this case, what you almost certainly want is:
fprintf(Archivo, "%d", id_doc);