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trunc, truncf, truncl

From cppreference.com
< c‎ | numeric‎ | math
 
 
 
Common mathematical functions
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Trigonometric and hyperbolic functions
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trunc
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Floating point manipulation functions
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Classification
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Macro constants
 
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.

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 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 <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] See also

computes largest integer not greater than the given value
(function) [edit]
(C99)(C99)
computes smallest integer not less than the given value
(function) [edit]
(C99)(C99)(C99)
rounds to nearest integer, rounding away from zero in halfway cases
(function) [edit]