Dynamic Memory Allocation is a mechanism in the C language. It allows programs to dynamically allocate and free memory space at runtime. By using dynamic memory allocation, a program can dynamically allocate memory as needed without having to determine the memory size at compile time. This allows programs to manage memory more flexibly and make efficient use of available system resources.

Here we will learn what is dynamic memory allocation in C language. The C programming language provides several functions for memory allocation and management. These functions can be found in the header file. The following functions are used for memory allocation.

##void *calloc(int num, int size );This function allocates an array of void free(void *address);This function releases a memory block specified by the address. void *malloc(int num);This function allocates an array of void *realloc(void *address, int newsize);This function reallocates memory and expands it to

Function	Description
	num elements, with the size of each element in bytes.
	num bytes and leaves it uninitialized.
	newsize.

Dynamic allocation of memory

When programming, if you know the size of the array, it is easy to define it as an array. For example, to store the name of any person, it can contain up to 100 characters, so you can define as follows -

char name[100];

But now let us consider a case where you don’t know the length of the text that needs to be stored, for example, You want to store a detailed description about a topic. Here we need to define a pointer to a character without defining how much memory is required, and then as needed, we can allocate memory as shown in the following example -

Sample code

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main() {
   char name[100];
   char *description;
   strcpy(name, "Adam");
   /* allocate memory dynamically */
   description = malloc( 200 * sizeof(char) );
   if( description == NULL ) {
      fprintf(stderr, "Error - unable to allocate required memory</p><p>");
   } else {
      strcpy( description, "Adam a DPS student in class 10th");
   }
   printf("Name = %s</p><p>", name );
   printf("Description: %s</p><p>", description );
}

Output

Name = Zara Ali
Description: Zara ali a DPS student in class 10th

The same program can be written using calloc(); the only problem is that you need to replace malloc with calloc as shown below -

calloc(200, sizeof(char));

So you have full control over allocating memory When passing any size value, unlike arrays, once the size of an array is defined, it cannot be changed.

Adjust the size of memory locations

The operating system will automatically release all memory allocated by your program when it comes out, but as a good practice, when you no longer need the memory , you should free the memory by calling the function free().

Alternatively, you can increase or decrease the size of the allocated memory block by calling the function realloc(). Let us check the above program again and use realloc() and free() functions -

Sample Code

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main() {
   char name[100];
   char *description;
   strcpy(name, "Adam");
   /* allocate memory dynamically */
   description = malloc( 30 * sizeof(char) );
   if( description == NULL ) {
      fprintf(stderr, "Error - unable to allocate required memory</p><p>");
   } else {
      strcpy( description, "Adam a DPS student.");
   }
   /* suppose you want to store bigger description */
   description = realloc( description, 100 * sizeof(char) );
   if( description == NULL ) {
      fprintf(stderr, "Error - unable to allocate required memory</p><p>");
   } else {
      strcat( description, "He is in class 10th");
   }
   printf("Name = %s</p><p>", name );
   printf("Description: %s</p><p>", description );
   /* release memory using free() function */
   free(description);
}

Output

Name = Adam
Description: Adam a DPS student.He is in class 10th

You can try the above example without Reallocate additional memory and the strcat() function will give an error due to lack of available memory in the description.

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