# std::trunc

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< cpp‎ | numeric‎ | math

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).

### Parameters

arg | - | floating point value

### 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
Argument

### 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

### 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.

### Example

Run this code

    #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

### See also

floor | nearest integer not greater than the given value (function)
ceil | nearest integer not less than the given value (function)
round lround llround (C++11)(C++11)(C++11) | nearest integer, rounding away from zero in halfway cases (function)
C documentation for trunc

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