Valgrind Error when creating an array of linked lists (for Hash Table Chaining)

问题

As an overview, I'm trying to create a battleship-like game in C, where ships are placed on a field.

Here is the error I am getting:

==11147== Invalid write of size 8
==11147==    at 0x400786: MakeField (battleship.c:34)
==11147==  Address 0x8 is not stack'd, malloc'd or (recently) free'd

Here is the relevant code:

struct piece{
    int x;
    int y;
    int direction;
    int length;
    char name;

};

struct node{
    struct piece boat;
    struct node *next;

};


struct field{
    int numBoats;
    struct node *array[numRows];
};

struct field *MakeField(void){
    struct field *f = NULL;
    struct node *temp = NULL;

    for(int i = 0; i < numRows; i++){
        f->array[i] = temp; <--- VALGRIND ERROR HERE
    }

    f->count = 0;
    return f;
}

Can anyone help with this issue?

回答1:

You are dereferencing a NULL poitner, you need to make your pointer point somewhere and to a valid somewhere, like this

struct field *f = malloc(sizeof(struct field));
if (f == NULL)
   return NULL;
/* ... continue your MakeField() function as it is */

don't forget to free(f) in the caller function.

By the way, valgrind is telling you that

Address 0x8 is not stack'd, malloc'd or (recently) free'd
                           ~~~^~~~

来源：https://stackoverflow.com/questions/28995317/valgrind-error-when-creating-an-array-of-linked-lists-for-hash-table-chaining