logb-logbf-logbl-logb-logbf.md

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logb, logbf, logbl, _logb, _logbf | Microsoft Docs		11/04/2016			cpp-standard-libraries		article	logb _logb _logbl logbf logbl	msvcrt.dll msvcr80.dll msvcr90.dll msvcr100.dll msvcr100_clr0400.dll msvcr110.dll msvcr110_clr0400.dll msvcr120.dll msvcr120_clr0400.dll ucrtbase.dll api-ms-win-crt-math-l1-1-0.dll	DLLExport	logb logbl _logb _logbf logbf	C++	_logbf function mantissas, floating-point variables logbf function _logb function exponent, floating-point numbers logbl function logb function floating-point functions floating-point functions, mantissa and exponent exponents and mantissas	780c4daa-6fe6-4fbc-9412-4c1ba1a1766f	13	corob-msft	corob	ghogen

logb, logbf, logbl, _logb, _logbf

Extracts the exponent value of a floating-point argument.

Syntax

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.

See Also

Floating-Point Support
frexp