std::source_location::current(3)

NAME
std::source_location::current - std::source_location::current

Synopsis
   static consteval source_location current() noexcept; (since C++20)
   Constructs a new source_location object corresponding to the location of the call
   site.

Parameters
   (none)

Return value
   If current() is invoked directly (via a function call that names current()), it
   returns a source_location object with implementation-defined values representing the
   location of the call. The values should be affected by the #line preprocessor
   directive in the same manner as the predefined macros __LINE__ and __FILE__.
   If current() is used in a default member initializer, the return value corresponds
   to the location of the constructor definition or aggregate initialization that
   initializes the data member.
   If current() is used in a default argument, the return value corresponds to the
   location of the call to current() at the call site.
   If current() is invoked in any other manner, the return value is unspecified.

Notes
   std::source_location::current typically requires compiler's built-in implementation.

Example
// Run this code
 #include <source_location>
 #include <iostream>
 struct src_rec {
     std::source_location srcl = std::source_location::current();
     int dummy = 0;
     src_rec(std::source_location loc = std::source_location::current()) :
         srcl(loc) // values of member refer to the location of the calling function
     {}
     src_rec(int i) : // values of member refer to this location
         dummy(i)
     {}
     src_rec(double) // values of member refer to this location
     {}
 };
 std::source_location src_clone(std::source_location a = std::source_location::current())
 {
     return a;
 }
 std::source_location src_make()
 {
     std::source_location b = std::source_location::current();
     return b;
 }
 int main()
 {
     src_rec srec0;
     src_rec srec1(0);
     src_rec srec2(0.0);
     auto s0 = std::source_location::current();
     auto s1 = src_clone(s0);
     auto s2 = src_clone();
     auto s3 = src_make();
     std::cout
         << srec0.srcl.line() << ' ' << srec0.srcl.function_name() << '\n'
         << srec1.srcl.line() << ' ' << srec1.srcl.function_name() << '\n'
         << srec2.srcl.line() << ' ' << srec2.srcl.function_name() << '\n'
         << s0.line() << ' ' << s0.function_name() << '\n'
         << s1.line() << ' ' << s1.function_name() << '\n'
         << s2.line() << ' ' << s2.function_name() << '\n'
         << s3.line() << ' ' << s3.function_name() << '\n';
 }

Possible output:
 31 int main()
 12 src_rec::src_rec(int)
 15 src_rec::src_rec(double)
 34 int main()
 34 int main()
 36 int main()
 25 std::source_location src_make()

See also
   constructor constructs a new source_location with implementation-defined values
                 (public member function)
   current obtains the current stacktrace or its given part
   [static] (public static member function of std::basic_stacktrace<Allocator>)