CODEWITHSUNDEEP
arrayscpointersdynamic-arrays
Bobby Li
Bobby Li

Reputation: 37

Return user defined structure to dynamic array element

I am trying to create a dynamic array to store a linked list in each element of the array. So I defined the linked list structure as below:

//data type for adjacent bus stop
typedef struct AdjStopNode
{
    int distance; //travel distance from the bus original stop to this adjcent stop
    int stopID;
    struct AdjStopNode *prev; //pointer to previous bus stop
    struct AdjStopNode *next; //pointer to next bus stop
} AdjStopNode;

AdjStopNode *newAdjStopNode(int distance, int stopID)
{
    AdjStopNode *newNode = (AdjStopNode *)malloc(sizeof(AdjStopNode));
    assert(newNode != NULL);
    newNode->distance = distance;
    newNode->stopID = stopID;
    newNode->next = NULL;
    return newNode;
}

typedef struct AdjStopList
{
    char stopname[20]; 
    int numOfAdjStp;   
    struct BusAtStopList *buslist;  
    struct AdjStopNode *first; //pointed at the first AdjBusStop of the linked list
    struct AdjStopNode *last;  //pointed at the first AdjBusStop of the linked list
} AdjStopList;

AdjStopList *newAdjStopList()
{
    AdjStopList *newList = (AdjStopList *)malloc(sizeof(AdjStopList));
    newList->buslist = newBusAtStopList();
    assert(newList != NULL);
    memset(newList, NULL, 20 * sizeof(newList[0]));
    newList->first = NULL;
    newList->last = NULL;
    newList->numOfAdjStp = 0;
    return newList;
}

Then I defined a dynamic array to store each AdjStopList as an element of the array is as below:

typedef struct BusNetwork
{
    int nBusStop; //number of bus stops in the newwork
    struct AdjStopList *array;
} BusNetwork;

My function to assign an empty AdjStopList to every element of the array is as below:

//n is the number of AdjStopList
void listToArray(int n)
{
    BusNetwork *newBN;
    newBN = malloc(sizeof(BusNetwork));
    assert(newBN != NULL);
    newBN->nBusStop = n;
    newBN->array = malloc(n * sizeof(AdjStopList)); //create an array of n number of dejacency lists
    for (int i = 0; i < n; i++)
    {
        newBN->array[i] = newAdjStopList();
    }
}

The above code gives me the error at newBN->array[i] = newAdjStopList() as

a value of type "AdjStopList *" cannot be assigned to an 
entity of type "struct AdjStopList" C/C++(513)

using VScode.

Could someone help me to fix this problem and explain to me why? Much appreciated.

Upvotes: 0

Views: 88

Answers (1)

Zoso
Zoso

Reputation: 3465

The type of newBN->array is struct AdjStopList * so the type of newBN->array[i] is struct AdjStopList but the return type fromnewAdjStopList() is struct AdjStopList*. So that should explain the error that you see where you are assigning a struct AdjStopList* to struct AdjStopList in the line

newBN->array[i] = newAdjStopList();

I believe you should change

typedef struct BusNetwork
{
    int nBusStop; //number of bus stops in the newwork
    struct AdjStopList *array;
} BusNetwork;

to

typedef struct BusNetwork
{
    int nBusStop; //number of bus stops in the newwork
    struct AdjStopList **array;
} BusNetwork;

So that array becomes an array of pointers to struct AdjStopList. Then that original assignment should work.

Upvotes: 1

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