C - Pointers and Structures

C Programming

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In this tutorial we will learn to use pointers with structures in C programming language.

We have learned how to create and work with structures in the Structures tutorial. Feel free to check that out.

Creating a structure

Lets start by creating a structure variable student as shown below.

// student structure
struct student {
  char id[15];
  char firstname[64];
  char lastname[64];
  float points;
};

Now we will create a student structure variable std. For this we will write the following code.

// student structure variable
struct student std;

Access the members of a structure

We know that to access a member of a structure we use the . operator.

In the following example we are accessing the members of the student structure.

printf("ID: %s\n", std.id);
printf("First Name: %s\n", std.firstname);
printf("Last Name: %s\n", std.lastname);
printf("Points: %f\n", std.points);

Creating pointer for structure

Following is the syntax to create a pointer for a structure.

struct tagName *ptrName;

So, to create a pointer for the student structure we will write the following code.

struct student *ptr;

Assigning structure variable to pointer

We use the following syntax to assign a structure variable address to a pointer.

ptrName = &structVarName;

In the following example we are assigning the address of the structure variable std to the structure pointer variable ptr. So, ptr is pointing at std.

ptr = &std;

Accessing the members of a structure via pointer

We use the arrow operator also known as member selection operator -> to access the members of a structure via pointer variable.

Following is the syntax for accessing members of a structure via pointer.

ptrName->member

In the following example we are accessing the firstname member of the student structure via pointer variable ptr.

printf("First Name: %s", ptr->firstname);

Complete code

#include <stdio.h>

int main(void) {
    
  // student structure
  struct student {
    char id[15];
    char firstname[64];
    char lastname[64];
    float points;
  };
  
  // student structure variable
  struct student std;
  
  // student structure pointer variable
  struct student *ptr = NULL;
  
  // assign std to ptr
  ptr = &std;
  
  // get student detail from user
  printf("Enter ID: ");
  scanf("%s", ptr->id);
  printf("Enter first name: ");
  scanf("%s", ptr->firstname);
  printf("Enter last name: ");
  scanf("%s", ptr->lastname);
  printf("Enter Points: ");
  scanf("%f", &ptr->points);
  
  // display result via std variable
  printf("\nResult via std\n");
  printf("ID: %s\n", std.id);
  printf("First Name: %s\n", std.firstname);
  printf("Last Name: %s\n", std.lastname);
  printf("Points: %f\n", std.points);
  
  // display result via ptr variable
  printf("\nResult via ptr\n");
  printf("ID: %s\n", ptr->id);
  printf("First Name: %s\n", ptr->firstname);
  printf("Last Name: %s\n", ptr->lastname);
  printf("Points: %f\n", ptr->points);
  
  return 0;
}

Output:

Enter ID: s01
Enter first name: Yusuf
Enter last name: Shakeel
Enter Points: 8.44

Result via std
ID: s01
First Name: Yusuf
Last Name: Shakeel
Points: 8.440000

Result via ptr
ID: s01
First Name: Yusuf
Last Name: Shakeel
Points: 8.440000

We can represent the student structure variable std in memory as follows.



So, when we create the structure variable std it takes up 147 bytes of memory space.

Member Data Type Size Memory Location
id char 15 bytes 1000 to 1014
firstname char 64 bytes 1015 to 1078
lastname char 64 bytes 1079 to 1142
points float 4 bytes 1143 to 1146

Next we have the pointer variable ptr that holds the memory address 1000 i.e., the memory address of the std structure variable. So, ptr is pointing at std.

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