C Programming
In this tutorial we will learn about calloc function to dynamically allocate memory in C programming language.
We use the calloc function to allocate memory at run time for derived data types like arrays and structures.
calloc
Using calloc function we can allocate multiple blocks of memory each of the same size and all the bytes will be set to 0. This is different from the malloc function from the previous tutorial which is used to allocate single block of memory space.
Following is the syntax of the calloc function to allocate memory dynamically.
ptr = (cast_type *) calloc (n, element_size);
Where, ptr is a pointer of type cast_type.
ptr
cast_type
n is the total block of contiguous spaces, each of size element_size to be allocated using the calloc function.
n
element_size
In the following example we are allocating memory space for 3 student structure variable.
// student structure struct student { char id[10]; char firstname[64]; char lastname[64]; int score; }; // new type typedef struct student candidate; // student structure pointer candidate *sptr; // variables int no_of_students = 3; // allocate memory blocks sptr = (candidate *) calloc (no_of_students, sizeof(candidate));
In the above code we are allocating 3 blocks of memory space each of size candidate structure i.e., 140 bytes.
#include <stdio.h> #include <stdlib.h> int main(void) { // student structure struct student { char id[10]; char firstname[64]; char lastname[64]; int score; }; // new type typedef struct student candidate; // student structure pointer candidate *sptr; candidate *tmp; // variables int no_of_students = 3; int i; // allocate memory blocks sptr = (candidate *) calloc (no_of_students, sizeof(candidate)); // get student details for(i = 0, tmp = sptr; i < no_of_students; i++, tmp++) { printf("Enter detail of student #%d\n", (i+1)); printf("ID: "); scanf("%s", tmp->id); printf("First Name: "); scanf("%s", tmp->firstname); printf("Last Name: "); scanf("%s", tmp->lastname); printf("Score: "); scanf("%d", &tmp->score); } // display student details printf("\n\nFollowing are the student details:\n\n"); for(i = 0, tmp = sptr; i < no_of_students; i++, tmp++) { printf("Detail of student #%d\n", (i+1)); printf("ID: %s\n", tmp->id); printf("First Name: %s\n", tmp->firstname); printf("Last Name: %s\n", tmp->lastname); printf("Score: %d\n", tmp->score); } // free memory location free(sptr); return 0; }
Output:
Enter detail of student #1 ID: s01 First Name: Yusuf Last Name: Shakeel Score: 8 Enter detail of student #2 ID: s02 First Name: Jane Last Name: Doe Score: 9 Enter detail of student #3 ID: s03 First Name: John Last Name: Doe Score: 7 Following are the student details: Detail of student #1 ID: s01 First Name: Yusuf Last Name: Shakeel Score: 8 Detail of student #2 ID: s02 First Name: Jane Last Name: Doe Score: 9 Detail of student #3 ID: s03 First Name: John Last Name: Doe Score: 7
We can represent the allocated memory as follows.
So, the three structures each of size 140 bytes are allocated memory location from address 1000 to 1139, 2000 to 2139 and 3000 to 3139.
The sptr structure pointer points at these memory locations.
sptr
We are using a temporary tmp structure pointer to access these allocated memory blocks.
tmp