C `stdlib.h` Library: Essential Functions for Memory Management and More

The <stdlib.h> library in C offers a range of functions that are vital for memory management, random number generation, string conversion to numbers, and various other utilities. Understanding these functions is essential for effective C programming.

C `stdlib.h` Library

The <stdlib.h> header provides a set of functions that are useful for memory management, random number generation, converting strings to numbers, and more.

Common C `stdlib` Functions

Here are some of the common functions provided by the stdlib.h library:

Function	Description
`abs()`	Returns the absolute (positive) value of an integer.
`atof()`	Converts a string to a double.
`atoi()`	Converts a string to an integer.
`atol()`	Converts a string to a long integer.
`atoll()`	Converts a string to a long long integer.
`calloc()`	Allocates dynamic memory and initializes it to zero.
`div()`	Performs integer division and returns the quotient and remainder.
`exit()`	Terminates the program.
`free()`	Deallocates dynamic memory.
`malloc()`	Allocates dynamic memory.
`qsort()`	Sorts the elements of an array.
`rand()`	Generates a random integer.
`realloc()`	Reallocates dynamic memory.
`srand()`	Seeds the random number generator.

Example: Memory Allocation and Random Numbers

Let’s see an example of how to use some stdlib.h functions to allocate memory dynamically, generate random numbers, and deallocate memory:

Example: Dynamic Memory Allocation and Random Numbers


#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main() {
    // Seed the random number generator
    srand(time(0));

    // Allocate memory for an array of 5 integers
    int *arr = (int *)malloc(5 * sizeof(int));
    if (arr == NULL) {
        printf("Memory allocation failed!\n");
        return 1;
    }

    // Fill the array with random numbers and print them
    for (int i = 0; i < 5; i++) {
        arr[i] = rand() % 100;  // Random number between 0 and 99
        printf("arr[%d] = %d\n", i, arr[i]);
    }

    // Deallocate memory
    free(arr);

    return 0;
}

Output:

Output


arr[0] = 23
arr[1] = 76
arr[2] = 45
arr[3] = 12
arr[4] = 89

This program allocates memory dynamically for 5 integers, fills the array with random numbers, and then deallocates the memory. Note the use of rand() to generate random numbers and free() to release the allocated memory.

C stdlib.h Library: Essential Functions for Memory Management and More