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.
#include <math.h> double rint(double x); float rintf(float x); long double rintl(long double x);
The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2017 defers to the ISO C standard.
These functions shall return the integral value (represented as a double) nearest x in the direction of the current rounding mode. The current rounding mode is implementation-defined.
If the current rounding mode rounds toward negative infinity, then rint() shall be equivalent to floor(). If the current rounding mode rounds toward positive infinity, then rint() shall be equivalent to ceil(). If the current rounding mode rounds towards zero, then rint() shall be equivalent to trunc(). If the current rounding mode rounds towards nearest, then rint() differs from round() in that halfway cases are rounded to even rather than away from zero.
These functions differ from the nearbyint(), nearbyintf(), and nearbyintl() functions only in that they may raise the inexact floating-point exception if the result differs in value from the argument.
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 non-zero, an error has occurred.
Upon successful completion, these functions shall return the integer (represented as a double precision number) nearest x in the direction of the current rounding mode. The result shall have the same sign as x.
If x is NaN, a NaN shall be returned.
If x is ±0 or ±Inf, x shall be returned.
No errors are defined.
The following sections are informative.
The integral value returned by these functions need not be expressible as an intmax_t. The return value should be tested before assigning it to an integer type to avoid the undefined results of an integer overflow.
abs(), ceil(), feclearexcept(), fetestexcept(), floor(), isnan(), nearbyint()
The Base Definitions volume of POSIX.1-2017, Section 4.20, Treatment of Error Conditions for Mathematical Functions, <math.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 original Standard can be obtained online at http://www.opengroup.org/unix/online.html .
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