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.
The 'c' in the name refers to "character" (stroustrup.com 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"; }
Output:
static constructor main function static destructor
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) |
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