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std::clog, std::wclog

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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 (as long as <iostream> is included).

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.

[edit] Example

#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

[edit] See also

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