function

trunc

     double trunc  (     double x);
      float truncf (      float x);
long double truncl (long double x);

     double trunc (     double x);
      float trunc (      float x);
long double trunc (long double x);
     double trunc (T x);           // additional overloads for integral types

Truncate value

Rounds x toward zero, returning the nearest integral value that is not larger in magnitude than x.

Header <tgmath.h> provides a type-generic macro version of this function.

Additional overloads are provided in this header (<cmath>) for the integral types: These overloads effectively cast x to a double before calculations (defined for T being any integral type).

Parameters

x: Value to truncate.

Return Value

The nearest integral value that is not larger in magnitude than x (as a floating-point value).

Example

/* round vs floor vs ceil vs trunc */
#include <stdio.h>      /* printf */
#include <math.h>       /* round, floor, ceil, trunc */

int main ()
{
  const char * format = "%.1f \t%.1f \t%.1f \t%.1f \t%.1f\n";
  printf ("value\tround\tfloor\tceil\ttrunc\n");
  printf ("-----\t-----\t-----\t----\t-----\n");
  printf (format, 2.3,round( 2.3),floor( 2.3),ceil( 2.3),trunc( 2.3));
  printf (format, 3.8,round( 3.8),floor( 3.8),ceil( 3.8),trunc( 3.8));
  printf (format, 5.5,round( 5.5),floor( 5.5),ceil( 5.5),trunc( 5.5));
  printf (format,-2.3,round(-2.3),floor(-2.3),ceil(-2.3),trunc(-2.3));
  printf (format,-3.8,round(-3.8),floor(-3.8),ceil(-3.8),trunc(-3.8));
  printf (format,-5.5,round(-5.5),floor(-5.5),ceil(-5.5),trunc(-5.5));
  return 0;
}

Output:


value   round   floor   ceil    trunc
-----   -----   -----   ----    -----
2.3     2.0     2.0     3.0     2.0
3.8     4.0     3.0     4.0     3.0
5.5     6.0     5.0     6.0     5.0
-2.3    -2.0    -3.0    -2.0    -2.0
-3.8    -4.0    -4.0    -3.0    -3.0
-5.5    -6.0    -6.0    -5.0    -5.0