CODEWITHSUNDEEP
cmalloc
user11819426
user11819426

Reputation:

Dynamic allocation of array in C that points to linked list

I have these structs and I want to initialize the PageTable and PageEntry. I want to create the shape below.

typedef struct PageEntry {
    unsigned int page_number;
    char mode;
    int count, R;
    struct PageEntry* next;
} PE;

typedef struct PageTable {
    int p_faults, reads, writes, disk_writes, maxFrames, curFrames;
    char* algorithm;
    struct PE **pe;
} PT;

enter image description here

I want to create a hash table, so I allocate for maxFrames PE*. My PageTable needs to have a pointer to the array and each element has to point to a linked list. Here is my init function:

PT *initialize_Table(int maxFrames, char *algorithm) {
    PT *ptr = malloc(sizeof(PT));   //Aloc

    ptr->p_faults = 0;
    ptr->reads = 0;
    ptr->writes = 0;
    ptr->curFrames = 0;
    ptr->disk_writes = 0;
    ptr->maxFrames = maxFrames;
    ptr->algorithm = malloc(strlen(algorithm) + 1);
    strcpy(ptr->algorithm, algorithm);
    ptr->pe = malloc((ptr->maxFrames) * sizeof(PE*));

    return ptr;
}

So Ptr->pe must be an array, but it isn't. I get this error:

enter image description here

What should I do ?

Upvotes: 1

Views: 78

Answers (1)

koder
koder

Reputation: 2103

No, ptr->pe is a pointer, not an array. You allocated memory for an array and you can index ptr->pe as if it was an array. So ptr->pe[i] is valid, if i is within range.

The contents of this freshly malloced piece of memory are undefined. Use memset to set it to all zeros, or use calloc (iso malloc) to allocate cleared memory.

Arrays in C are second rate citizens. You can declare them , initialize them and query their size with sizeof, but you can't do anything else with them. For all other purposes an array variable decays (or is treated as) a pointer to the first element.

Upvotes: 1

Related Questions