logb, logbf, logbl, _logb, _logbf

Article
04/28/2015

Extracts the exponent value of a floating-point argument.

double logb(
   double x 
);
float logb(
   float x 
); // C++ only
long double logb(
   long double x 
); // C++ only 
float logbf(
   float x 
);
long double logbl(
   long double x 
);
double _logb(
   double x 
);
float _logbf(
   float x 
);

Parameters

x
A floating-point value.

Return Value

logb returns the unbiased exponent value of x as a signed integer represented as a floating-point value.

Remarks

The logb functions extract the exponential value of the floating-point argument x, as though x were represented with infinite range. If the argument x is denormalized, it is treated as if it were normalized.

Because C++ allows overloading, you can call overloads of logb that take and return float or long double values. In a C program, logb always takes and returns a double.

Input	SEH exception	Matherr exception
± QNAN,IND	None	_DOMAIN
± 0	ZERODIVIDE	_SING

Requirements

Routine	Required header
_logb	<float.h>
logb, logbf, logbl, _logbf	<math.h>

For more compatibility information, see Compatibility.

Libraries

All versions of the C run-time libraries.

.NET Framework Equivalent

Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.

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