Hello we are trying to crate a small expert system for a assignment for our university and the part which creates nodes using rete by reading characteristics from a file gives us a core dumped, we have problems findind where the problem is because we are new to all of this programming in C, if anyone could help we would be very grateful.

Thanks a lot
code:
# include <string.h>
#include <stdio.h>
#include <stdlib.h>


typedef struct node{
char atributo[20];
char simbolo[20];
char output;
struct node* children;
struct node* next;

} *punt_nodo,nodo;

void leer(char c, FILE* f)
{
char i;
if(i!=EOF) i=fgetc(f);
while ((i!=c)&&(i!=EOF)) i=fgetc(f);
}

punt_nodo creacionnodos (FILE*archivo)
{
punt_nodo nodoaux=(punt_nodo)malloc(sizeof(nodo));
punt_nodo nodoaux2=(punt_nodo)malloc(sizeof(nodo));
char c;
leer('!',archivo);
fscanf(archivo,"%s",nodoaux->simbolo);
leer(':',archivo);
fscanf(archivo,"%s",nodoaux->children->simbolo);
if ((nodoaux->children)!=NULL){
nodoaux2=nodoaux->children;

while((c=fgetc(archivo))!='&'){
leer(':', archivo);
fscanf(archivo, "%s",nodoaux2->next->simbolo);
if ((nodoaux2->next)!=NULL){nodoaux2=nodoaux2->next;}}}

return nodoaux;
}


int main(void)
{FILE* f=fopen("caracteristicas.txt","r");
punt_nodo nodo1=creacionnodos(f);
printf("%s",nodo1->simbolo);
}

Here you trust the input data to not overflow simbolo. Very dangerous, easily breakable.
At least specify the field width like so: "%19s".

Now you use nodoaux->children which has never been inititlaized. Which means fscanf will attempt to write to some random memory address. Hence the segfault.

Thanks a lot we have managed to fix the seg error although we still have some problems compiling it,

Thank you

You have some additional (typical) problems with this function:

• i and c should be int, not char to avoid signed/unsigned problems and to be able to match EOF. (Note that fgetc() returns int, not char.)
• The first if() doesn't make sense, as i has never been initialized. In C, you first read the character, then check if it was EOF.
• The variable naming is unusual. Not an error, but makes code more difficult to read. I'd suggest to use c instead of i and to use a more descriptive name instead of c.
• You might want to return a value to indicate if the function terminated successfully or because it encountered EOF.

So all in all you'd come up with something like: