std::clog, std::wclog

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Defined in header <iostream>

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extern std::ostream clog;

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extern std::wostream wclog;

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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 constructed before the first constructor of a static object is called and they are guaranteed to outlive the last destructor of a static object, so that it is always possible to write to std::clog in user code.

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.


#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

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