std::cerr, std::wcerr

Header: <iostream>

The global objects std::cerr and std::wcerr control output to a stream buffer of implementation-defined type (derived from std::streambuf and std::wstreambuf, respectively), associated with the standard C error output stream stderr.

# Declarations

extern std::ostream cerr;

extern std::wostream wcerr;

# Notes

The ‘c’ in the name refers to “character” (stroustrup.com FAQ); cerr means “character error (stream)” and wcerr means “wide character error (stream)”.

# Example

#include <chrono>
#include <iostream>
#include <thread>
using namespace std::chrono_literals;
 
void f()
{
    std::cout << "Output from thread...";
    std::this_thread::sleep_for(2s);
    std::cout << "...thread calls flush()" << std::endl;
}
 
int main()
{
    std::jthread t1{f};
    std::this_thread::sleep_for(1000ms);
    std::clog << "This output from main is not tie()'d to cout\n";
    std::cerr << "This output is tie()'d to cout\n";
}

# Defect reports

DR	Applied to	Behavior as published	Correct behavior
LWG 455	C++98	std::cerr.tie() andstd::wcerr.tie() returned null pointers	they return &std::cout and&std::wcout respectively