std::cerr, std::wcerr - cppreference.com (original) (raw)

| Defined in header | | | | ----------------------------------------------------------------------------- | --- | | | extern std::ostream cerr; | (1) | | | extern std::wostream wcerr; | (2) | |

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.

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 is included before the object is defined).

Unless std::ios_base::sync_with_stdio(false) has been issued, it is safe to concurrently access these objects from multiple threads for both formatted and unformatted output.

Once initialized, (std::cerr.flags() & unitbuf) != 0 (same for std::wcerr) meaning that any output sent to these stream objects is immediately flushed to the OS (via std::basic_ostream::sentry's destructor).

In addition, std::cerr.tie() returns &std::cout (same for std::wcerr and std::wcout), meaning that any output operation on std::cerr first executes std::cout.flush() (via std::basic_ostream::sentry's constructor).

[edit] Notes

The 'c' in the name refers to "character" (stroustrup.com FAQ); cerr means "character error (stream)" and wcerr means "wide character error (stream)".

[edit] Example

Output to stderr via std::cerr flushes out the pending output on std::cout, while output to stderr via std::clog does not.

Possible output:

This output from main is not tie()'d to cout Output from thread...This output is tie()'d to cout ...thread calls flush()

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit] See also

| | initializes standard stream objects (public member class of std::ios_base) [edit] | | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | writes to the standard C error stream stderr(global object)[edit] | | | writes to the standard C output stream stdout(global object)[edit] | | | expression of type FILE* associated with the input streamexpression of type FILE* associated with the output streamexpression of type FILE* associated with the error output stream (macro constant) [edit] |