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Determines the natural logarithm of the absolute value of the gamma function of the specified value.
Syntax
double lgamma( double x );
float lgammaf( float x );
long double lgammal( long double x );
#define lgammal(X) // Requires C11 or higher
float lgamma( float x ); //C++ only
long double lgamma( long double x ); //C++ only
Parameters
x
The value to compute.
Return value
If successful, return the natural logarithm of the absolute value of the gamma function of x.
| Issue | Return |
|---|---|
x = NaN |
NaN |
x = ±0 |
+INFINITY |
x= negative integer |
+INFINITY |
| ±INFINITY | +INFINITY |
| pole error | +HUGE_VAL, +HUGE_VALF, or +HUGE_VALL |
| overflow range error | ±HUGE_VAL, ±HUGE_VALF, or ±HUGE_VALL |
Errors are reported as specified in _matherr.
Remarks
Because C++ allows overloading, you can call overloads of lgamma that take and return float and long double types. In a C program, unless you're using the <tgmath.h> macro to call this function, lgamma always takes and returns a double.
If you use the <tgmath.h> lgamma() macro, the type of the argument determines which version of the function is selected. See Type-generic math for details.
If x is a rational number, this function returns the logarithm of the factorial of (x - 1).
By default, this function's global state is scoped to the application. To change this behavior, see Global state in the CRT.
Requirements
| Function | C header | C++ header |
|---|---|---|
lgamma, lgammaf, lgammal |
<math.h> | <cmath> |
lgamma macro |
<tgmath.h> |
For more compatibility information, see Compatibility.