std::trunc,std::truncf,std::truncl
| Common mathematical functions | |||||||||||||||||||||||||||||||
| Mathematical special functions(C++17) | |||||||||||||||||||||||||||||||
| Mathematical constants(C++20) | |||||||||||||||||||||||||||||||
| Basic linear algebra algorithms(C++26) | |||||||||||||||||||||||||||||||
| Data-parallel types (SIMD)(C++26) | |||||||||||||||||||||||||||||||
| Floating-point environment(C++11) | |||||||||||||||||||||||||||||||
| Complex numbers | |||||||||||||||||||||||||||||||
Numeric array (valarray) | |||||||||||||||||||||||||||||||
| Pseudo-random number generation | |||||||||||||||||||||||||||||||
| Bit manipulation(C++20) | |||||||||||||||||||||||||||||||
| Saturation arithmetic(C++26) | |||||||||||||||||||||||||||||||
| Factor operations | |||||||||||||||||||||||||||||||
|
| ||||||||||||||||||||||||||||||
| Interpolations | |||||||||||||||||||||||||||||||
|
| ||||||||||||||||||||||||||||||
| Generic numeric operations | |||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||
| C-style checked integer arithmetic | |||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||
| Nearest integer floating point operations | |||||||||||||||||||||||||||||||||||||||||
|
| ||||||||||||||||||||||||||||||||||||||||
| Floating point manipulation functions | |||||||||||||||||||||||||||||||||||||||||
|
| ||||||||||||||||||||||||||||||||||||||||
| Classification and comparison | |||||||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||||||
| Types | |||||||||||||||||||||||||||||||||||||||||
| Macro constants | |||||||||||||||||||||||||||||||||||||||||
|
| ||||||||||||||||||||||||||||||||||||||||
Defined in header <cmath> | ||
| (1) | ||
float trunc(float num); double trunc(double num); | (until C++23) | |
constexpr/*floating-point-type*/ trunc(/*floating-point-type*/ num); | (since C++23) | |
float truncf(float num); | (2) | (since C++11) (constexpr since C++23) |
longdouble truncl(longdouble num); | (3) | (since C++11) (constexpr since C++23) |
SIMD overload(since C++26) | ||
Defined in header <simd> | ||
template</*math-floating-point*/ V> constexpr/*deduced-simd-t*/<V> | (S) | (since C++26) |
Additional overloads(since C++11) | ||
Defined in header <cmath> | ||
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)S) The SIMD overload performs an element-wise std::trunc onv_num.
| (since C++26) |
A) Additional overloads are provided for all integer types, which are treated asdouble. | (since C++11) |
Contents |
[edit]Parameters
| num | - | floating-point or integer value |
[edit]Return value
If no errors occur, the nearest integer value not greater in magnitude thannum (in other words,num rounded towards zero) is returned.
[edit]Error handling
Errors are reported as specified inmath_errhandling.
If the implementation supports IEEE floating-point arithmetic (IEC 60559),
- The currentrounding mode has no effect.
- Ifnum is ±∞, it is returned, unmodified.
- Ifnum is ±0, it is returned, unmodified.
- Ifnum is NaN, NaN is returned.
[edit]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 (includingstd::intmax_t), when stored in an integer variable.
Theimplicit conversion from floating-point to integral types also rounds towards zero, but is limited to the values that can be represented by the target type.
The additional overloads are not required to be provided exactly as(A). They only need to be sufficient to ensure that for their argumentnum of integer type,std::trunc(num) has the same effect asstd::trunc(static_cast<double>(num)).
[edit]Example
#include <cmath>#include <initializer_list>#include <iostream> int main(){constauto 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(doubleconst x: data)std::cout<<"trunc("<< x<<") == "<< std::trunc(x)<<'\n';}
Possible output:
trunc(+2.7) == +2trunc(-2.9) == -2trunc(+0.7) == +0trunc(-0.9) == -0trunc(+0) == +0trunc(+0) == +0trunc(-inf) == -inftrunc(+inf) == +inftrunc(-nan) == -nantrunc(+nan) == +nan
[edit]See also
(C++11)(C++11) | nearest integer not greater than the given value (function)[edit] |
(C++11)(C++11) | nearest integer not less than the given value (function)[edit] |
(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)(C++11) | nearest integer, rounding away from zero in halfway cases (function)[edit] |
C documentation fortrunc | |
