
NEXTAFTER(3P) POSIX Programmer's Manual NEXTAFTER(3P)
PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of
this interface may differ (consult the corresponding Linux manual page for details of
Linux behavior), or the interface may not be implemented on Linux.
NAME
nextafter, nextafterf, nextafterl, nexttoward, nexttowardf, nexttowardl  next repre
sentable floatingpoint number
SYNOPSIS
#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 shall compute the next repre
sentable floatingpoint value following x in the direction of y. Thus, if y is less than
x, nextafter() shall return the largest representable floatingpoint number less than x.
The nextafter(), nextafterf(), and nextafterl() functions shall return y if x equals y.
The nexttoward(), nexttowardf(), and nexttowardl() functions shall be equivalent to the
corresponding nextafter() functions, except that the second parameter shall have type long
double and the functions shall return y converted to the type of the function if x equals
y.
An application wishing to check for error situations should set errno to zero and call
feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if errno is non
zero or fetestexcept(FE_INVALID  FE_DIVBYZERO  FE_OVERFLOW  FE_UNDERFLOW) is nonzero,
an error has occurred.
RETURN VALUE
Upon successful completion, these functions shall return the next representable floating
point value following x in the direction of y.
If x== y, y (of the type x) shall be returned.
If x is finite and the correct function value would overflow, a range error shall occur
and +HUGE_VAL, +HUGE_VALF, and +HUGE_VALL (with the same sign as x) shall be returned
as appropriate for the return type of the function.
If x or y is NaN, a NaN shall be returned.
If x!= y and the correct function value is subnormal, zero, or underflows, a range error
shall occur, and either the correct function value (if representable) or 0.0 shall be
returned.
ERRORS
These functions shall fail if:
Range Error
The correct value overflows.
If the integer expression (math_errhandling & MATH_ERRNO) is nonzero, then errno shall be
set to [ERANGE]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non
zero, then the overflow floatingpoint exception shall be raised.
Range Error
The correct value is subnormal or underflows.
If the integer expression (math_errhandling & MATH_ERRNO) is nonzero, then errno shall be
set to [ERANGE]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non
zero, then the underflow floatingpoint exception shall be raised.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
On error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling &
MATH_ERREXCEPT) are independent of each other, but at least one of them must be nonzero.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
feclearexcept(), fetestexcept(), the Base Definitions volume of IEEE Std 1003.12001, Sec
tion 4.18, Treatment of Error Conditions for Mathematical Functions, <math.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1, 2003 Edition, Standard for Information Technology  Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 20012003 by
the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and The Open Group
Standard, the original IEEE and The Open Group Standard is the referee document. The orig
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 NEXTAFTER(3P) 
