Allocating memory for Structure Array within a Structure

Question

I have an application to work, where i need to use an array of structure type as a member of structure . I have created models with structure but as you can see I need a member as an array inside the contact structure(dynamically depending on the user's input). I am allocating the size for it in the getContacts function by passing a variable named contactPersonLength from main,but as soon as the getContacts returns to main value of contactPersonLength variable changes and garbage value gets printed in main. So i am having trouble passing the varible to print function. Please tell me where i am wrong and how to allocate size for array which is a structure member

struct address
{
    char *name,*street,*district;
    int doorNo;
};

struct contactPerson
{
    char *name,*contactNumber;
};

struct contact
{
    char *firstName,*lastName,*emailId;
    struct address billingAddress;
    struct address shippingAddress;
    struct contactPerson contactPersons[];
};

void getContacts(struct contact *contacts,int n,int contactPersonLength)
{
    int isSame,i,j;
    for(i=0;i<n;i++)
    {
        printf(".......Enter Contact Details %d  ........\n",i+1);
        contacts[i].firstName = (char *)malloc(sizeof(char));
        printf("Enter the First Name");
        scanf("%s",contacts[i].firstName);

        contacts[i].lastName = (char *)malloc(sizeof(char));
        printf("Enter the Last Name");
        scanf("%s",contacts[i].lastName);

        contacts[i].emailId = (char *)malloc(sizeof(char));
        printf("Enter the email id");
        scanf("%s",contacts[i].emailId);

        printf(".....Billing address Details.....\n");
        contacts[i].billingAddress.name = (char *)malloc(sizeof(char));
        printf("Enter the name");
        scanf("%s",contacts[i].billingAddress.name);

        printf("Enter the DoorNo");
        scanf("%d",&contacts[i].billingAddress.doorNo);

        contacts[i].billingAddress.street = (char *)malloc(sizeof(char));
        printf("Enter the Street name");
        scanf("%s",contacts[i].billingAddress.street);


        contacts[i].billingAddress.district = (char *)malloc(sizeof(char));
        printf("Enter the District");
        scanf("%s",contacts[i].billingAddress.district);

        printf(".....Shipping Address Details....\n");
        printf("Is your Shipping Address same as Billing Address Press 1 Or else Press 0");
        scanf("%d",&isSame);
        if(isSame==1)
        {
            contacts[i].shippingAddress = contacts[i].billingAddress;
        }
        else
        {
            contacts[i].shippingAddress.name = (char *)malloc(sizeof(char));
            printf("Enter the name");
            scanf("%s",contacts[i].shippingAddress.name);

            printf("Enter the DoorNo");
            scanf("%d",&contacts[i].shippingAddress.doorNo);

            contacts[i].shippingAddress.street = (char *)malloc(sizeof(char));
            printf("Enter the Street name");
            scanf("%s",contacts[i].shippingAddress.street);

            contacts[i].shippingAddress.district = (char *)malloc(sizeof(char));
            printf("Enter the District");
            scanf("%s",contacts[i].shippingAddress.district);
        }

        printf(" ContactPersonLength %d \n",contactPersonLength);
        contacts[i].contactPersons[contactPersonLength];
        for(j=0;j<contactPersonLength;j++)
        {
            printf(".....ContactPerson %d.....\n",j+1);
            contacts[i].contactPersons[j].name = (char *)malloc(sizeof(char));
            printf("Enter Contact Person Name");
            scanf("%s",contacts[i].contactPersons[j].name);

            contacts[i].contactPersons[j].contactNumber = (char *)malloc(sizeof(char));
            printf("Enter Contact Person Contact Number");
            scanf("%s",contacts[i].contactPersons[j].contactNumber);
        }
    }

}



void main()
{   
    struct contact contacts[n];

    getContacts(contacts,n,contactPersonLen);
}

Answer 1

I would suggest that your function should work as follows:

char buffer[256];
for(i=0;i<n;i++)
{
    printf(".......Enter Contact Details %d  ........\n",i+1);
    do {
        printf("Enter the First Name");
    } while (scanf("%255s",buffer)!=1);
    contacts[i].firstName = malloc(strlen(buffer)+1);
    strcpy(contacts[i].firstName, buffer);
    //...etc

So you use a single buffer to get the input, then allocate memory exactly the size of the input, plus a terminating null character, then copy the buffer to that memory and reuse the buffer for the next input.

Notes: the size of a char is always 1, so sizeof(char) is not needed. Also, the result of malloc should not be cast.

You ask the input in a do...while loop and check that scanf was able to read input. In scanf, the format specifier limits the input to 255 characters so the buffer will not overflow.

Answer 2

(char *)malloc(sizeof(char)); allocates only one byte of memory. If you want to store a string, say 20 chars long, the code is: (char *)malloc(sizeof(char) * 20 + 1); //explicitly showed +1 for clarity, based on comment. (char *)malloc(sizeof(char) * 20 + 1); //explicitly showed +1 for clarity, based on comment.

---

EDIT

Generally it is a good idea to set the maximum possible size of the array in malloc . But if the size is too large, and/or you are concerned about memory, do the following:

contacts[i].firstName = (char *)malloc(sizeof(char) * MAX_POSSIBLE_SIZE);
printf("Enter the First Name");
scanf("%s",contacts[i].firstName);
char *temp = (char *)realloc(contacts[i].firstName, strlen(contacts[i].firstName) + 1);
if(temp!=NULL)  contacts[i].firstName = temp;

Do this for every string.