trunc, truncf, truncl

Determines the nearest integer that is less than or equal to the specified floating-point value.


double trunc( double x );
long double truncl( long double x );
#define trunc(X) // Requires C11 or higher

long double trunc( long double x ); //C++ only
float trunc( float x ); //C++ only


The value to truncate.

Return value

If successful, the functions return an integer value of x, rounded towards zero.

Otherwise, the functions may return one of the following values:

Issue Return
x = ┬▒INFINITY x
x = ┬▒0 x
x = NaN NaN

Errors are reported as specified in _matherr.


Because C++ allows overloading, you can call overloads of trunc that take and return float and long double types. In a C program, unless you're using the <tgmath.h> macro to call this function, trunc always takes and returns a double.

If you use the <tgmath.h> trunc() macro, the type of the argument determines which version of the function is selected. See Type-generic math for details.

Because the largest floating-point values are exact integers, this function won't overflow on its own. However, you may cause the function to overflow by returning a value into an integer type.

You can also round down by implicitly converting from floating-point to integral; however, doing so is limited to the values that can be stored in the target type.


Function C header C++ header
trunc, truncf, truncl <math.h> <cmath>
trunc macro <tgmath.h>

For more compatibility information, see Compatibility.

See also

Alphabetical function reference
floor, floorf, floorl
ceil, ceilf, ceill
round, roundf, roundl