##### cppreference.com

##### Search

Create account

##### Namespaces

- Page
- Discussion

##### Variants

##### Views

- View
- Edit
- History

##### Actions

# trunc, truncf, truncl

From cppreference.com
< c‎ | numeric‎ | math

Defined in header `<math.h>` |  |
float truncf( float arg ); | (1) | (since C99)
double trunc( double arg ); | (2) | (since C99)
long double truncl( long double arg ); | (3) | (since C99)
Defined in header `<tgmath.h>` |  |
#define trunc( arg ) | (4) | (since C99)

1-3) Computes the nearest integer not greater in magnitude than `arg`.
4) Type-generic macro: If `arg` has type long double, `truncl` is called. Otherwise, if `arg` has integer type or the type double, `trunc` is called. Otherwise, `truncf` is called.

### [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
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 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

Run this code

    #include <math.h>
    #include <stdio.h>
    int main(void)
    {
        printf("trunc(+2.7) = %+.1f\n", trunc(2.7));
        printf("trunc(-2.7) = %+.1f\n", trunc(-2.7));
        printf("trunc(-0.0) = %+.1f\n", trunc(-0.0));
        printf("trunc(-Inf) = %+f\n",   trunc(-INFINITY));
    }

Possible output:

    trunc(+2.7) = +2.0
    trunc(-2.7) = -2.0
    trunc(-0.0) = -0.0
    trunc(-Inf) = -inf

### [edit] References

- C11 standard (ISO/IEC 9899:2011):

  - 7.12.9.8 The trunc functions (p: 253-254)

  - 7.25 Type-generic math <tgmath.h> (p: 373-375)

  - F.10.6.8 The trunc functions (p: 528)

- C99 standard (ISO/IEC 9899:1999):

  - 7.12.9.8 The trunc functions (p: 234)

  - 7.22 Type-generic math <tgmath.h> (p: 335-337)

  - F.9.6.8 The trunc functions (p: 464)

### [edit] See also

floor floorf floorl (C99)(C99) | computes largest integer not greater than the given value (function) [edit]
ceil ceilf ceill (C99)(C99) | computes smallest integer not less than the given value (function) [edit]
round lround llround (C99)(C99)(C99) | rounds to nearest integer, rounding away from zero in halfway cases (function) [edit]
C++ documentation for trunc

Retrieved from "http://en.cppreference.com/mwiki/index.php?title=c/numeric/math/trunc&oldid=77352"