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std::trunc

From cppreference.com
< cpp‎ | numeric‎ | math
 
 
 
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Defined in header <cmath>
float       trunc( float arg );
(1) (since C++11)
double      trunc( double arg );
(2) (since C++11)
long double trunc( long double arg );
(3) (since C++11)
double      trunc( Integral arg );
(4) (since C++11)
1-3) Computes the nearest integer not greater in magnitude than arg.
4) A set of overloads or a function template accepting an argument of any integral type. Equivalent to 2) (the argument is cast to double).

Contents

[edit] Parameters

arg - floating point value

[edit] Return value

If no errors occur, the nearest integer value not greater in magnitude than arg (in other words, arg rounded towards zero) is returned.

Return value
math-trunc.svg
Argument

[edit] 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 arg is ±∞, it is returned, unmodified
  • If arg is ±0, it is returned, unmodified
  • If arg 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 (including std::intmax_t), when stored in an integer variable.

The implicit 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.

[edit] Example

#include <cmath>
#include <iostream>
int main()
{
    std::cout << std::fixed
              << "trunc(+2.7) = " << std::trunc(+2.7) << '\n'
              << "trunc(-2.9) = " << std::trunc(-2.9) << '\n'
              << "trunc(-0.0) = " << std::trunc(-0.0) << '\n'
              << "trunc(-Inf) = " << std::trunc(-INFINITY) << '\n';
}

Possible output:

trunc(+2.7) = 2.000000
trunc(-2.9) = -2.000000
trunc(-0.0) = -0.000000
trunc(-Inf) = -inf

[edit] See also

nearest integer not greater than the given value
(function) [edit]
nearest integer not less than the given value
(function) [edit]
(C++11)(C++11)(C++11)
nearest integer, rounding away from zero in halfway cases
(function) [edit]
C documentation for trunc