std::source_location(3)

NAME
std::source_location - std::source_location

Synopsis
   Defined in header <source_location>
   struct source_location; (since C++20)
   The std::source_location class represents certain information about the source code,
   such as file names, line numbers, and function names. Previously, functions that
   desire to obtain this information about the call site (for logging, testing, or
   debugging purposes) must use macros so that predefined macros like __LINE__ and
   __FILE__ are expanded in the context of the caller. The std::source_location class
   provides a better alternative.
   std::source_location meets the DefaultConstructible, CopyConstructible,
   CopyAssignable and Destructible requirements. Lvalue of std::source_location meets
   the Swappable requirement.
   Additionally, the following conditions are true:
     * std::is_nothrow_move_constructible_v<std::source_location>,
     * std::is_nothrow_move_assignable_v<std::source_location>, and
     * std::is_nothrow_swappable_v<std::source_location>.
   It is intended that std::source_location has a small size and can be copied
   efficiently.
   It is unspecified whether the copy/move constructors and the copy/move assignment
   operators of std::source_location are trivial and/or constexpr.

Member functions
         Creation
   constructor constructs a new source_location with implementation-defined values
                 (public member function)
   current constructs a new source_location corresponding to the location of the
   [static] call site
                 (public static member function)
         Field access
   line return the line number represented by this object
                 (public member function)
   column return the column number represented by this object
                 (public member function)
   file_name return the file name represented by this object
                 (public member function)
   function_name return the name of the function represented by this object, if any
                 (public member function)

Notes
      Feature-test macro Value Std Feature
   __cpp_lib_source_location 201907L (C++20) Source-code information capture
                        (std::source_location)

Example
// Run this code
 #include <iostream>
 #include <source_location>
 #include <string_view>
 void log(const std::string_view message,
          const std::source_location location =
                std::source_location::current())
 {
     std::clog << "file: "
               << location.file_name() << '('
               << location.line() << ':'
               << location.column() << ") `"
               << location.function_name() << "`: "
               << message << '\n';
 }
 template<typename T>
 void fun(T x)
 {
     log(x); // line 20
 }
 int main(int, char*[])
 {
     log("Hello world!"); // line 25
     fun("Hello C++20!");
 }

Possible output:
 file: main.cpp(25:8) `int main(int, char**)`: Hello world!
 file: main.cpp(20:8) `void fun(T) [with T = const char*]`: Hello C++20!

See also
                    changes the source code's line number and, optionally, the current
   #line file name
                    (preprocessing directive)
   stacktrace_entry representation of an evaluation in a stacktrace
   (C++23) (class)