Change array value within LinkedList

Question

I'm trying to make a program that calculates the probability of a given caracter goes after a certain sequence of caracters. To do so i'm using a struct node, as implemented bellow:

typedef struct node
{
    struct node* prox[nchars];
    int* ocorrencias;
    int n;
} node;

The n refers to the number of times the specific node apeared. The pointer "ocorrencias" is actually an array that has nchars size, and each entry represents the number of times a given caracter has appeared after the current node. To initialize each node i use the following function:

void AlocaNode(node* qualquer){
    //Função usada para inicializar as variaveis de um node
    qualquer = malloc(sizeof(node));
    qualquer->n = 0;
    qualquer->ocorrencias = (int *)calloc(nchars, sizeof(int));
}

My problem is when i try to change the values of the node. I must have tried a duzen of different algoritms to update the ocorrencias array. The last one i tried is written bellow. pos is an intenger, and i'm sure it has a valid value.

//Pegamos a posição do caracter no array
pos = retornaPos(letra);

//Atualizamos a ocorrencias no node
int *prt = malloc(sizeof(int));
prt = &atual->ocorrencias;
*(prt+pos) = *(prt+pos) + 1;

//E o número de vezes que o node apareceu
atual->n++;

//Verificamos se o node atual já foi alocado
if (atual->prox[pos] == NULL){
      AlocaNode(atual->prox[pos]);
}

//E atualizamos o nosso node para apontar para o próximo
atual = atual->prox[pos];

What am i doing wrong? How do i update its value?

Answer 1

Your AlocaNode loses the memory allocated, because the variable qualquer goes out of scope after the function exits:

void AlocaNode(node* qualquer) {
    qualquer = malloc(sizeof(node));
    qualquer->n = 0;
    qualquer->ocorrencias = (int *)calloc(nchars, sizeof(int));
}

The node from the calling function isn't updated. Instead, you could pass a double pointer to node:

void AlocaNode(node **qualquer) {
    *qualquer = malloc(sizeof(node));
    (*qualquer)->n = 0;
    (*qualquer)->ocorrencias = calloc(nchars, sizeof(int));
}

and call like this:

node qualquer;

AlocaNode(&qualquer);

Another possibility is to return the new node from the function:

node *AlocaNode(void) {
    node *qualquer = malloc(sizeof(node));

    (*qualquer)->n = 0;
    (*qualquer)->ocorrencias = calloc(nchars, sizeof(int));
    return qualquer;
}

and call like this:

node qualquer = AlocaNode();

(I prefer the second variant.)

Answer 2

int *prt = malloc(sizeof(int));
prt = &atual->ocorrencias;

Memory leak, you reserve space for prt but this address is replaced on the next line, furthermore atual->ocorrencias is already a pointer (don't use the address-of operator & )

Change to:

int *prt = atual->ocorrencias;