std::clog, std::wclog

< cpp‎ | io
Input/output library
I/O manipulators
C-style I/O
(deprecated in C++98)
File I/O
String I/O
Array I/O
(deprecated in C++98)
(deprecated in C++98)
(deprecated in C++98)
Synchronized Output
Error category interface
Defined in header <iostream>
extern std::ostream clog;
extern std::wostream wclog;

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.


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


#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";


static constructor
main function
static destructor

See also

initializes standard stream objects
(public member class of std::ios_base)
writes to the standard C error stream stderr, unbuffered
(global object)
writes to the standard C output stream stdout
(global object)