#include <math.h> long lround(double x); long lroundf(float x); long lroundl(long double x);
These functions shall round their argument to the nearest integer value, rounding halfway cases away from zero, regardless of the current rounding direction.
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.
If x is NaN, a domain error shall occur and an unspecified value is returned.
If x is +Inf, a domain error shall occur and an unspecified value is returned.
If x is -Inf, a domain error shall occur and an unspecified value is returned.
If the correct value is positive and too large to represent as a long, an unspecified value shall be returned. On systems that support the IEC 60559 Floating-Point option, a domain shall occur; otherwise, a domain error may occur.
If the correct value is negative and too large to represent as a long, an unspecified value shall be returned. On systems that support the IEC 60559 Floating-Point option, a domain shall occur; otherwise, a domain error may occur.
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [EDOM]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be raised.
These functions may fail if:
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [EDOM]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be raised.
The following sections are informative.
The Base Definitions volume of POSIX.1-2017, Section 4.20, Treatment of Error Conditions for Mathematical Functions, <math.h>
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