取 CGFloat 的绝对值

Question

How can I do that? I tried the abs() but it only works for int's. Is there a built in way to do so?

CGFloat flo = -123;
abs(flo)

this returns 0

Answer 1

Use fabs()

CGFloat f = -123.4f;
CGFloat g = fabs(f);

CGFloat is defined as a double on 64-bit machines, and float on 32-bit machines. If you are targeting both 64 and 32 bit than this answer gets more complicated, but is still correct.

You want to use fabs() because it works on double datatypes which are larger than float . On 32-bit, assigning the return value of fabs() (which is a double ) into a CGFloat (which is a float ) is ok ONLY if you are taking the absolute value of a CGFloat or float . You would potentially overflow a 32-bit CGFloat if you try to store the absolute value of a large double number. In short, 64-bit is fine, and on 32-bit don't mix and match double and CGFloat and you'll be fine.

The ABS() macro apparently can have side-effects on some compilers.

Answer 2

For 64/32 bit system

#if CGFLOAT_IS_DOUBLE
    CGFloat g = fabs(flo);
#else
    CGFloat g = fabsf(flo);
#endif

Answer 3

I normally just use the ABS macro, as far as I can tell, it works regardless of which system you're on or which primitive you're using.

CGFloat x = -1.1;
double y = -2.1;
NSInteger z = -5;

x = ABS(x);
y = ABS(y);
z = ABS(z);

Answer 4

Small addition:

CGFloat g = fabs(f);

This will result in a casting warning, because fabs() returns a double value. To get a float value back, you need to use fabsf().

CGFloat g = fabsf(f);

Answer 5

fabs is depreciated. The signature of abs is now generic with this signature

/// Returns the absolute value of the given number.
///
/// The absolute value of `x` must be representable in the same type. In
/// particular, the absolute value of a signed, fixed-width integer type's
/// minimum cannot be represented.
///
///     let x = Int8.min
///     // x == -128
///     let y = abs(x)
///     // Overflow error
///
/// - Parameter x: A signed number.
/// - Returns: The absolute value of `x`.
@inlinable public func abs<T>(_ x: T) -> T where T : Comparable, T : SignedNumeric