#include <math.h>
long lrint(double x);
long lrintf(float x);
long lrintl(long double x);
These functions shall round their argument to the nearest integer value, rounding according to 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.
Upon successful completion, these functions shall return the rounded integer value.
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, a domain error shall occur and an unspecified value is returned.
If the correct value is negative and too large to represent as a long, a domain error shall occur and an unspecified value is returned.
These functions shall 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.
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 non-zero.
These functions provide floating-to-integer conversions. They round according to the current rounding direction. If the rounded value is outside the range of the return type, the numeric result is unspecified and the invalid floating-point exception is raised. When they raise no other floating-point exception and the result differs from the argument, they raise the inexact floating-point exception.
feclearexcept() , fetestexcept() , llrint() , the Base Definitions volume of IEEE Std 1003.1-2001, Section 4.18, Treatment of Error Conditions for Mathematical Functions, <math.h>