logb, logbf, logbl, _logb, _logbf

 

The new home for Visual Studio documentation is Visual Studio 2017 Documentation on docs.microsoft.com.

The latest version of this topic can be found at logb, logbf, logbl, _logb, _logbf.

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.

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

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.

InputSEH exceptionMatherr exception
± QNAN,INDNone_DOMAIN
± 0ZERODIVIDE_SING
RoutineRequired header
_logb<float.h>
logb, logbf, logbl, _logbf<math.h>

For more compatibility information, see Compatibility.

All versions of the C run-time libraries.

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

Floating-Point Support
frexp

Show: