- next representable double-precision floating-point number
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);
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.
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.
These functions will fail if:
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.
The correct value underflows.
If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, the underflow floating-point exception is raised.
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.
See attributes(5) for descriptions of the following attributes: