std::trunc, std::truncf, std::
Defined in header <cmath>
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| (1) | ||
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float trunc (
float num )
;
double trunc ( double num ); |
(until C++23) | |
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constexpr
/*floating-point-type*/
trunc ( /*floating-point-type*/ num ) ; |
(since C++23) | |
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float truncf( float num );
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(2) | (since C++11) (constexpr since C++23) |
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long
double truncl(
long
double num )
;
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(3) | (since C++11) (constexpr since C++23) |
SIMD overload (since C++26) |
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Defined in header <simd>
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template
<
/*math-floating-point*/ V >
constexpr /*deduced-simd-t*/<V> |
(S) | (since C++26) |
Additional overloads (since C++11) |
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Defined in header <cmath>
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template
<
class Integer >
double trunc ( Integer num ) ; |
(A) | (constexpr since C++23) |
std::trunc for all cv-unqualified floating-point types as the type of the parameter.
(since C++23)
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S) The SIMD overload performs an element-wise
std::trunc on v_num.
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(since C++26) |
A) Additional overloads are provided for all integer types, which are treated as double.
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(since C++11) |
Parameters
| num | - | floating-point or integer value |
Return value
If no errors occur, the nearest integer value not greater in magnitude than num (in other words, num
Error handling
Errors are reported as specified in math_errhandling.
If the implementation supports IEEE floating-point arithmetic (IEC 60559),
- The current rounding mode has no effect.
- If num is ±∞, it is returned, unmodified.
- If num is ±0, it is returned, unmodified.
- If num is NaN, NaN is returned.
Notes
FE_INEXACT may be (but isn't required to be) raised when truncating a non-integer finite value.
The largest representable floating-point values are exact integers in all standard floating-point formats, so this function never overflows on its own; however the result may overflow any integer type (including std::intmax_t
The additional overloads are not required to be provided exactly as (A). They only need to be sufficient to ensure that for their argument num of integer type, std::trunc(num) has the same effect as std:: trunc ( static_cast < double > (num) )
Example
#include <cmath> #include <initializer_list> #include <iostream> int main() { const auto data = std::initializer_list<double> { +2.7, -2.9, +0.7, -0.9, +0.0, 0.0, -INFINITY, +INFINITY, -NAN, +NAN }; std::cout << std::showpos; for (double const x : data) std::cout << "trunc(" << x << ") == " << std::trunc(x) << '\n'; }
Possible output:
trunc(+2.7) == +2 trunc(-2.9) == -2 trunc(+0.7) == +0 trunc(-0.9) == -0 trunc(+0) == +0 trunc(+0) == +0 trunc(-inf) == -inf trunc(+inf) == +inf trunc(-nan) == -nan trunc(+nan) == +nan
See also
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(C++11)(C++11)
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nearest integer not greater than the given value (function) |
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(C++11)(C++11)
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nearest integer not less than the given value (function) |
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(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
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nearest integer, rounding away from zero in halfway cases (function) |
C documentation for trunc
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