Content-type: text/html Man page of nextafter

# nextafter

Section: Mathematical Library Functions (3M)
Updated: 12 Jul 2006

## NAME

nextafter, nextafterf, nextafterl, nexttoward, nexttowardf, nexttowardl - next representable double-precision floating-point number

## SYNOPSIS

```c99 [ flag... ] file... -lm [ library... ]
#include <math.h>
```

double nextafter(double x, double y);

float nextafterf(float x, float y);

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

double nexttoward(double x, long double y);

float nexttowardf(float x, long double y);

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

## DESCRIPTION

The nextafter(), nextafterf(), and nextafterl() functions compute the next representable floating-point value following x in the direction of y. Thus, if y is less than x, nextafter() returns the largest representable floating-point number less than x. The nextafter(), nextafterf(), and nextafterl() functions return y if x equals y.

The nexttoward(), nexttowardf(), and nexttowardl() functions are equivalent to the corresponding nextafter() functions, except that the second parameter has type long double and the functions return y converted to the type of the function if x equals y.

## RETURN VALUES

Upon successful completion, these functions return the next representable floating-point value following x in the direction of y.

If x == y, y (of the type x) is returned.

If x is finite and the correct function value would overflow, a range error occurs and ±HUGE_VAL, ±HUGE_VALF, and ±HUGE_VALL (with the same sign as x) is returned as appropriate for the return type of the function.

If x or y is NaN, a NaN is returned.

If x != y and the correct function value is subnormal, zero, or underflows, a range error occurs and either the correct function value (if representable) or 0.0 is returned.

## ERRORS

These functions will fail if:

Range Error The correct value overflows.

If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, the overflow floating-point exception is raised.

The nextafter() function sets errno to ERANGE if the correct value would overflow.

Range Error The correct value underflows.

If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, the underflow floating-point exception is raised.

## USAGE

An application wanting to check for exceptions should call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an exception has been raised. An application should either examine the return value or check the floating point exception flags to detect exceptions.

An application can also set errno to 0 before calling nextafter(). On return, if errno is non-zero, an error has occurred. The nextafterf(), nextafterl(). nexttoward(), nexttowardf(), and nexttowardl() functions do not set errno.

## ATTRIBUTES

See attributes(5) for descriptions of the following attributes:

 ATTRIBUTE TYPE ATTRIBUTE VALUE Interface Stability Standard MT-Level MT-Safe

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUES
ERRORS
USAGE
ATTRIBUTES