malloc()
The word malloc refers to memory allocation. This function reserves a single block of memory of the specified number of bytes. It returns a pointer of void type that can be cast into any form. Since it is not initialised during allocation, it is filled with some garbage value until initialisation.
Syntax:
ptr = (castType*) malloc(size);
// ptr is a pointer variable
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Example:
#include <stdio.h>
#include <stdlib.h>
int main() {
int n = 4;
int i, *ptr, sum = 0;
ptr = (int*) malloc(n * sizeof(int));
// if memory is not allocated
if(ptr == NULL) {
printf("Memory not allocated.");
exit(0);
}
printf("Enter elements: ");
for(i = 0; i < n; ++i) {
scanf("%d", ptr + i);
sum += *(ptr + i);
}
printf("Sum = %d", sum);
return 0;
}
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Output:
Enter elements:
3
5
7
9
Sum = 24
The above example shows the use of malloc function to perform dynamic memory allocation and store an array of 4 integers.
calloc()
The name calloc refers to contiguous allocation. This function allocates n blocks of memory dynamically to store n values and initialises all bits to zero.
Syntax:
ptr = (castType*)calloc(n, size);
// ptr is a pointer variable
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Example:
#include <stdio.h>
#include <stdlib.h>
int main() {
int n = 4;
int i, *ptr, sum = 0;
ptr = (int*) calloc(n, sizeof(int));
if(ptr == NULL) {
printf("Memory not allocated.");
exit(0);
}
printf("Enter elements: ");
for(i = 0; i < n; ++i) {
scanf("%d", ptr + i);
sum += *(ptr + i);
}
printf("Sum = %d", sum);
return 0;
}
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Output:
Enter elements:
4
5
6
7
Sum = 22
The above example shows the use of calloc function to allocate memory dynamically and store an array of 4 integers.
realloc()
The realloc() method is used when the present allocated memory is not sufficient. It resizes an existing allocated memory block. It first deallocates the old object and reallocates it with the newly specified size. If the new size is lesser than the old size, the contents of the newly allocated memory will be the same as before. However, if the bytes in the newly created object goes beyond the old size, the values of the object will be indeterminate.
Syntax:
ptr = realloc(ptr, n*sizeof(data_type);
// ptr is a pointer variable
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Example:
#include <stdio.h>
#include <stdlib.h>
int main() {
int *ptr, i , n = 4, m = 6;
ptr = (int*) malloc(n * sizeof(int));
printf("Addresses of memory to hold 4 integers:\n");
for(i = 0; i < n; ++i)
printf("%pc\n",ptr + i);
printf("\nResizing allocated memory to hold 6 integers... ");
// re-allocation
ptr = realloc(ptr, m * sizeof(int));
printf("Addresses of newly allocated memory:\n");
for(i = 0; i < m; ++i)
printf("%pc\n", ptr + i);
return 0;
}
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Output:
Addresses of memory to hold 4 integers:
0x7efc01150560c
0x7efc01150564c
0x7efc01150568c
0x7efc0115056cc
Resizing allocated memory to hold 6 integers...
Addresses of newly allocated memory:
0x7efc01150560c
0x7efc01150564c
0x7efc01150568c
0x7efc0115056cc
0x7efc01150570c
0x7efc01150574c
You can also read about the dynamic arrays in c, and Tribonacci Series
free()
The free() method is used to dynamically deallocate the memory. It helps avoid wastage of memory space by freeing unused/unwanted memory resources.
Syntax:
free(ptr);
//ptr is a pointer to the memory block that is to be freed
You can also try this code with Online C Compiler
Example:
#include <stdio.h>
#include <stdlib.h>
int main() {
int n = 4;
int i, *ptr, sum = 0;
ptr = (int*) calloc(n, sizeof(int));
if(ptr == NULL) {
printf("Memory not allocated.");
exit(0);
}
free(ptr);
return 0;
}
You can also try this code with Online C Compiler
Also see, Short int in C Programming
Frequently Asked Questions
What is the difference between calloc and malloc?
A malloc and calloc are functions used for memory allocation and management. The memory allocated by calloc is initialised with 0, while malloc does not initialise the allocated memory. The malloc function takes one argument, but calloc takes two.
What is a pointer variable?
A pointer is a variable that contains the address of another variable in the memory. It points to a data type (like int ) of the same type and is created with the * operator. The size of a pointer variable depends on the compiler.
What is the difference between dynamic and static memory allocation?
Static memory allocation allows fixed memory size after allocation while Dynamic memory allocation allows changes in the memory size after allocation.
Conclusion
This article extensively discusses Dynamic memory allocation in C. We hope that this blog has helped you enhance your knowledge about the different ways of allocating memory dynamically in C. If you would like to learn more, check out our articles on the Coding Ninjas Library. Do upvote our blog to help other ninjas grow. Happy Coding!
Related Links:
Dynamic Memory
Ternary Operator in C
Difference between static and dynamic memory allocation
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