static_cast浮点到枚举

Question

Let's say that I have an enumeration:

enum FRACTION {
    WHOLE,
    HALF,
    THIRD,
    QUARTER,
    FRACTION_SIZE
};

Now I want to take a floating point denominator of a fraction and cast it, so I want:

• [ 0.5F , 1.5F ) to map to WHOLE
• [ 1.5F , 2.5F ) to map to HALF
• [ 2.5F , 3.5F ) to map to THIRD
• [ 3.5F , 4.5F ) to map to QUARTER

Given float foo I cannot do this:

 
 
 
 
  
  
  static_cast<FRACTION>(round(foo))
 
 
  

Because I get the error:

error C2440: static_cast : cannot convert from float to FRACTION

I can do 2 static_cast s: static_cast<FRACTION>(static_cast<int>(round(foo))) Or I could probably work out a map solution with lower_bound . But both of those seem ugly. Does c++ not have a provision for more direct conversion?

Answer 1

You want a function to do it:

FRACTION classifyDenominator(float denominator) {
  assert(denominator >= 0.5f && denominator < 4.5f);
  denominator -= 0.5f;
  return static_cast<FRACTION>(int(denominator));
}