trunc, truncf, truncl (original) (raw)

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

Syntax

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

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

Parameters

x
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:

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.

Requirements

For more compatibility information, see Compatibility.

See also

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