logstream.h File Reference

#include <deal.II/base/config.h>
#include <deal.II/base/enable_observer_pointer.h>
#include <deal.II/base/exceptions.h>
#include <deal.II/base/observer_pointer.h>
#include <deal.II/base/thread_local_storage.h>
#include <cmath>
#include <memory>
#include <sstream>
#include <stack>
#include <string>

Go to the source code of this file.

Classes
class	LogStream
class	LogStream::Prefix

Functions
template<typename T >
LogStream &	operator<< (LogStream &log, const T &t)

Variables
LogStream	deallog

Function Documentation

operator<<()

template<typename T >

LogStream & operator<< ( LogStream &  log, const T &  t  )

inline

Output a constant something through LogStream:

Note

We declare this operator as a non-member function so that it is possible to overload it with more specialized templated versions under C++11 overload resolution rules

Definition at line 405 of file logstream.h.

Variable Documentation

deallog

LogStream deallog

extern

The standard log object of deal.II. Take a look at the documentation of the LogStream class for more information, as well as below.

The deallog variable (which stands for deal-log, not de-allog) represents a stream to which some parts of the library write output. For example, iterative solvers will generate diagnostics (starting residual, number of solver steps, final residual).

The output of deallog can be written to the console, to a file, or both. Both are disabled by default since over the years we have learned that a program should only generate output when a user explicitly asks for it. But this can be changed, and to explain how this can be done, we need to explain how deallog works: When individual parts of the library want to log output, they open a "context" or "section" into which this output will be placed. At the end of the part that wants to write output, one exits this section again. Since a function may call another one from within the scope where this output section is open, output may in fact be nested hierarchically into these sections. The LogStream class of which deallog is a variable calls each of these sections a "prefix" because all output is printed with this prefix at the left end of the line, with prefixes separated by colons. There is always a default prefix called "DEAL" (a hint at deal.II's history as the successor of a previous library called "DEAL" and from which the LogStream class is one of the few pieces of code that were taken into deal.II).

By default, logstream only outputs lines with zero prefixes – i.e., all output is disabled because the default "DEAL" prefix is always there. But one can set a different maximal number of prefixes for lines that should be output to something larger, by calling LogStream::depth_console() with an integer argument. Let's assume you call it with 2 as argument. This means that for all screen output a context that has pushed one additional prefix beyond the default "DEAL" is allowed to print its output to the screen ("console"), whereas all further nested sections that would have three or more prefixes active would write to deallog, but deallog does not forward this output to the screen.

Definition at line 36 of file logstream.cc.