std::clog,std::wclog (3) - Linux Manuals

std::clog,std::wclog: std::clog,std::wclog

NAME

std::clog,std::wclog - std::clog,std::wclog

Synopsis

Defined in header <iostream>
extern std::ostream clog; (1)
extern std::wostream wclog; (2)

The global objects std::clog and std::wclog control output to a stream buffer of implementation-defined type (derived from std::streambuf), associated with the standard C output stream stderr, but, unlike std::cerr/std::wcerr, these streams are not automatically flushed and not automatically tie()'d with cout.
These objects are guaranteed to be initialized during or before the first time an object of type std::ios_base::Init is constructed and are available for use in the constructors and destructors of static objects with ordered_initialization (as long as <iostream> is included before the object is defined).
Unless sync_with_stdio(false) has been issued, it is safe to concurrently access these objects from multiple threads for both formatted and unformatted output.

Notes

The 'c' in the name refers to "character" (stroustrup.com_FAQ); clog means "character log" and wclog means "wide character log"

Example

// Run this code

  #include <iostream>

  struct Foo {
      int n;
      Foo() {
         std::clog << "static constructor\n";
      }
      ~Foo() {
         std::clog << "static destructor\n";
      }
  };

  Foo f; // static object

  int main()
  {
      std::clog << "main function\n";
  }

Output:

  static constructor
  main function
  static destructor