C check input floats (-0.0f, 0.0f)-CodePudding

I am currently trying to build a program which prints an input float value to binary.

The first bit is 0 if positive or 1 if negative, but with an input value of e.g.: -0.0g my if statement always prints 1, also for a positive input. How would I check that correctly?

string sign = "sign: ";
if(value <= -0.0f)
 sign.append("1\n");
else if (value >= 0.0f)
 sign.append("0\n");

...

CodePudding user response：

0.0 and -0.0 have the same value, yet different signs.

value <= -0.0f is true for value as 0.0 and -0.0. @MSalters

To distinguish the sign, use std::signbit(). @john

if(std::signbit(value)) {
  sign.append("1\n");
} else {
  sign.append("0\n");
}

Note that signbit() also applies to infinities and NaN.

Even though std::signbit reports "Along with std::copysign, std::signbit is one of the only two portable ways to examine the sign of a NaN.", there may be others.