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
);
#define logb(X) // Requires C11 or higher
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's 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, unless you're using the <tgmath.h> macro to call this function, logb always takes and returns a double.
If you use the logb macro from <tgmath.h>, the type of the argument determines which version of the function is selected. See Type-generic math for details.
| Input | SEH exception | _matherr exception |
|---|---|---|
| ± QNaN, IND | None | _DOMAIN |
| ± 0 | ZERODIVIDE |
_SING |
By default, this function's global state is scoped to the application. To change this behavior, see Global state in the CRT.
Requirements
| Routine | Required header |
|---|---|
_logb |
<float.h> |
logb, logbf, logbl, _logbf |
<math.h> |
logb macro |
<tgmath.h> |
For more compatibility information, see Compatibility.
Libraries
All versions of the C run-time libraries.