std::student_t_distribution<RealType>:: n

From cppreference.com
RealType n ( ) const ;
(since C++11)

Returns the n distribution parameter (number of the degrees of freedom) the distribution was constructed with. The default value is 1.0 .

Parameters

(none)

Return value

Floating point value identifying the degrees of freedom of the distribution.

See also

(C++11)
gets or sets the distribution parameter object
(public member function)