path: courses/c-course/stdlib.md

- **fileName**: stdlib
- **Created on**: 2024-07-10 18:58:02

stdlib is library in c for handle the allocate the memory and manage the memory and free it and refer to Dynamic memory allocation in c .

• malloc

• calloc

• realloc

• free

1- malloc :

The “malloc” or “memory allocation” method in C is used to dynamically allocate a single large block of memory with the specified size. It returns a pointer of type void which can be cast into a pointer of any form. It doesn’t Initialize memory at execution time so that it has initialized each block with the default garbage value initially
****ptr = (int*) malloc(100 * sizeof(int));****

2- calloc() method

1. “calloc” or “contiguous allocation” method in C is used to dynamically allocate the specified number of blocks of memory of the specified type. it is very much similar to malloc() but has two different points and these are:
2. It initializes each block with a default value ‘0’.
3. It has two parameters or arguments as compare to malloc().
   `ptr = (int*)calloc(n, sizeof(int));

3- free

“free” method in C is used to dynamically de-allocate the memory. The memory allocated using functions malloc() and calloc() is not de-allocated on their own. Hence the free() method is used, whenever the dynamic memory allocation takes place. It helps to reduce wastage of memory by freeing it.
free(ptr)

4- realloc() method

“realloc” or “re-allocation” method in C is used to dynamically change the memory allocation of a previously allocated memory. In other words, if the memory previously allocated with the help of malloc or calloc is insufficient, realloc can be used to dynamically re-allocate memory. re-allocation of memory maintains the already present value and new blocks will be initialized with the default garbage value.
ptr = realloc(ptr, newSize);

example:

#include <stdio.h>
#include <stdlib.h>
int main()
{
    // This pointer will hold the
    // base address of the block created
    int* ptr;
    int n, i;
    // Get the number of elements for the array
    n = 5;
    printf("Enter number of elements: %d\n", n);
    // Dynamically allocate memory using calloc()
    ptr = (int*)calloc(n, sizeof(int));
    // Check if the memory has been successfully
    // allocated by malloc or not
    if (ptr == NULL) {
        printf("Memory not allocated.\n");
        exit(0);
    }
    else {
        // Memory has been successfully allocated
        printf("Memory successfully allocated using calloc.\n");
        // Get the elements of the array
        for (i = 0; i < n; ++i) {
            ptr[i] = i + 1;
        }
        // Print the elements of the array
        printf("The elements of the array are: ");
        for (i = 0; i < n; ++i) {
            printf("%d, ", ptr[i]);
        }
        // Get the new size for the array
        n = 10;
        printf("\n\nEnter the new size of the array: %d\n", n);
        // Dynamically re-allocate memory using realloc()
        ptr = (int*)realloc(ptr, n * sizeof(int));
          if (ptr == NULL) {
          printf("Reallocation Failed\n");
          exit(0);
        }
        // Memory has been successfully allocated
        printf("Memory successfully re-allocated using realloc.\n");
        // Get the new elements of the array
        for (i = 5; i < n; ++i) {
            ptr[i] = i + 1;
        }
        // Print the elements of the array
        printf("The elements of the array are: ");
        for (i = 0; i < n; ++i) {
            printf("%d, ", ptr[i]);
        }
        free(ptr);
    }
    return 0;
}

difference between malloc and calloc:

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