c,list,pointers,struct,char , Fill value by value a char *


Fill value by value a char *

Question:

Tag: c,list,pointers,struct,char

I'm trying to fill a char *info inside a struct nodo;

This is struct :

struct nodo {
char *info;
struct nodo *prec;
struct nodo *succ;
};
typedef struct nodo nodo;

And this is whole function :

nodo *q,*t = NULL,*head = NULL;
int i, nodi=0 ;
char *c = a, *k = a;

while ( *c != '\0') {
    if (*c == ' ')
        nodi++;
    c++;
}

for (i = 0; nodi != 0; i++) {
    if (i == 0){
        head = CreateFirstNodo();
        t = head;}
    if (i == 1)
        q = CreateSecondNodo(head);
    else
        q = CreateNNodo(head);
    nodi--;

}


char *k = a;
int i = 0;
while ( *k != '\0' )
{        
    if (*k == ' ' )
    {
        head = head->succ; 
        i = 0;
    }
    head->info[i] = *k; // ERROR EXC BAD ACCESS 
    i++;
    k++;
}
return t;
}

k is a char* and should scroll the char[] to which is assigned and should copy any of his values to the proper place in head->info[i] which is char *info in struct

if k hits a space, the nodo goes to the next nodo and the 'i' become 0 again since i need a word filled in each nodo.

BUT this code shows error EXC BAD ACCESS in the marked line.

Here are the 3 CreateNodo functions:

nodo *CreateFirstNodo() {
nodo *q;

q = malloc(sizeof(nodo));
q->prec = NULL;
q->succ = NULL;

return q;
}

nodo *CreateSecondNodo(nodo *head) {
nodo *q;

q = malloc(sizeof(nodo));
q->succ = NULL;
q->prec = head;
head->succ = q;

return q;
}


nodo *CreateNNodo(nodo *head) {

nodo *q;

while (head->succ != NULL) {
    head = head ->succ;
}

q = malloc(sizeof(nodo));
q->succ = NULL;
q->prec = head;
head->succ = q;

return q;

EDIT: sorry for lacking code.


Answer:

The reason you get EXC BAD ACCESS is because you never actually allocate memory for info. In your struct nodo you have info defined to be a pointer to a character, but you never have any memory allocated for it.

Depending on how big your input could be you could either do char info[256] (or whatever size you want) or you could calloc the amount of space you want in Createxxxx functions.

Additionally, you really only need one Create function. I would do something like this:

nodo *CreateNodo(nodo *head)
{
    nodo *q;

    q = calloc(1, sizeof(nodo));
    if (q) {
        //assume info should be 256 chars
        q->info = calloc(256, sizeof(char));
        if (!q->info) {
            free(q);
            return NULL;
        }
        q->succ = NULL;
        q->prec = NULL;

        if (head) {
            while (head->succ != NULL) {
                head = head->succ;
            }
            q->prec = head;
            head->succ = q;
        }

    return (q);
}

That way you only have 1 function to debug/fix.


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