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.arg | - | floating point 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

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

`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.

#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

- 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)

(C99)(C99) | computes largest integer not greater than the given value (function) |

(C99)(C99) | computes smallest integer not less than the given value (function) |

(C99)(C99)(C99) | rounds to nearest integer, rounding away from zero in halfway cases (function) |

C++ documentation for `trunc` |

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