In C, the nextafter() is a standard library function that is used to find the next representable floating-point value after a given number in the direction of another specified number.

In this article, we will learn how to use the nextafter() function in C and its variant for different floating point types.

Syntax of nextafter() in C

double nextafter(double x, double y);

Parameters

The nextafter() function in C takes two parameters:

• x: The starting point (a floating-point number).
• y: The direction point (a floating-point number).

Return Value

• The return value is the next representable floating-point value after x in the direction of y.
• If x equals y, the function returns y.

Variants of nextafter in C

The nextafter() function comes in three variations, catering to different floating-point types:

nextafterf() for float

float nextafterf(float x, float y);

nextafterl() for long double

long double nextafterl(long double x, long double y);

Examples of nextafter() in C

Example 1: Program to demonstrate how to use the nextafter() function

// C Program to demonstrate the nextafter() function

#include <math.h>
#include <stdio.h>

int main()
{
    double x = 1.0, y = 2.0;
    double result = nextafter(x, y);

    // Print the result
    printf("The next representable value after %.2lf "
           "towards %.2lf is: %.17g\n",
           x, y, result);

    return 0;
}

The next representable value after 1.00 towards 2.00 is: 1.0000000000000002

Time Complexity: O(1)
Auxiliary Space: O(1)

Example 2: Program to demonstrate the use of the variants of the nextafter() function

// C program to demonstrate the nextafter() function for
// different data types

#include <math.h>
#include <stdio.h>

int main()
{
    double x1 = 1.0, y1 = 2.0;
    float x2 = 2.0f, y2 = 4.0f;
    long double x3 = 3.0l, y3 = 5.0l;

    // nextafter function for double
    double result1 = nextafter(x1, y1);

    // nextafterf function for float
    float result2 = nextafterf(x2, y2);

    // nextafterl function for long double
    long double result3 = nextafterl(x3, y3);

    // Print the results
    printf("The next representable value after %.2lf "
           "towards %.2lf is: %.17g\n",
           x1, y1, result1);
    printf("The next representable value after %.2f "
           "towards %.2f is: %.8g\n",
           x2, y2, result2);
    printf("The next representable value after %.2Lf "
           "towards %.2Lf is: %.21Lg\n",
           x3, y3, result3);

    return 0;
}

Output

The next representable value after 1.00 towards 2.00 is: 1.0000000000000002
The next representable value after 2.00 towards 4.00 is: 2.0000002
The next representable value after 3.00 towards 5.00 is: 3.00000000000000000022

Time Complexity: O(1)
Auxiliary Space: O(1)