C structs and Pointers

In this tutorial, you’ll learn to use pointers to access to individuals from structs in C programming. You will likewise learn to dynamically allocate memory of struct types.

Before you learn about how pointers can be used with structs, be sure to check these tutorials:

C Pointers

C struct

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C Pointers to struct

Here’s how you can create pointers to structs.

struct name {
    member1;
    member2;
    .
    .
};

int main()
{
    struct name *ptr, salman;
}

Here, ptr is a pointer to struct.

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Example: Access members using Pointer

To access members of a structure using pointers, we use the -> operator.

#include <stdio.h>
struct person
{
   int age;
   float weight;
};

int main()
{
    struct person *personPtr, person1;
    personPtr = &person1;   

    printf("Enter age: ");
    scanf("%d", &personPtr->age);

    printf("Enter weight: ");
    scanf("%f", &personPtr->weight);

    printf("Displaying:\n");
    printf("Age: %d\n", personPtr->age);
    printf("weight: %f", personPtr->weight);

    return 0;
}

In this example, the address of person1 is stored in the personPtr pointer using personPtr = &person1;.

Now, you can access the members of person1 using the personPtr pointer.

By the way,

personPtr->age is equivalent to (*personPtr).age
personPtr->weight is equivalent to (*personPtr).weight

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Dynamic memory allocation of structs

Before you continue this area, we prescribe you to check C dynamic memory allocation.

Once in awhile, the number of struct variables you declared might be insufficient. You may need to dispense memory during run-time. Here’s the way you can accomplish this in C programming.

Example: Dynamic memory allocation of structs

#include <stdio.h>
#include <stdlib.h>
struct person {
   int age;
   float weight;
   char name[30];
};

int main()
{
   struct person *ptr;
   int i, n;

   printf("Enter the number of persons: ");
   scanf("%d", &n);

   // allocating memory for n numbers of struct person
   ptr = (struct person*) malloc(n * sizeof(struct person));

   for(i = 0; i < n; ++i)
   {
       printf("Enter first name and age respectively: ");

       // To access members of 1st struct person,
       // ptr->name and ptr->age is used

       // To access members of 2nd struct person,
       // (ptr+1)->name and (ptr+1)->age is used
       scanf("%s %d", (ptr+i)->name, &(ptr+i)->age);
   }

   printf("Displaying Information:\n");
   for(i = 0; i < n; ++i)
       printf("Name: %s\tAge: %d\n", (ptr+i)->name, (ptr+i)->age);

   return 0;
}

When you run the program, the output will be:

Enter the number of persons:  2
Enter first name and age respectively:  salman 22
Enter first name and age respectively:  haroon 24
Displaying Information:
Name: salman	Age: 22
Name: haroon	Age: 24

In the above example, n number of struct factors are made where n is entered by the user.

To designate the memory for n number of struct individual, we used,

ptr = (struct person*) malloc(n * sizeof(struct person));

Then, we used the ptr pointer to access the elements of the person.

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Please feel free to give your comment if you face any difficulty here.

Structure and Union