How do I set std::ios_base flags like std::left in boost log 2.0?

Question

I have an application which makes extensive use of boost log 2.0. Now I would like to set some default flags for that application like `std::setprecision(std::numeric_limits::digits10 + 1)`, `std::scientific` and `std::left`. But how do I do that? One approach is creating a logger at the very beginning of my main function and creating a dummy log message. This permanently sets the desired flags. But is there no nicer way to do this? edit in reply to: "OP should show actual code." I have a global Logging singleton, called L: ``` class L{ public: enum severity_level { dddebug, ddebug, debug, control, iiinfo, iinfo, info, result, warning, error, critical }; typedef boost::log::sources::severity_channel_logger< severity_level, // the type of the severity level std::string // the type of the channel name > logger_t; typedef boost::log::sinks::synchronous_sink< boost::log::sinks::text_ostream_backend > text_sink; boost::shared_ptr< text_sink > sink_; static L& get(); static boost::s…

Accepted Answer

@rhashimoto makes a good point about how your current solution will break down with multiple threads/concurrent logging operations. I feel the best solution is to define your own logging macros to replace `BOOST_LOG_SEV` which have the stream modifiers included, like this:

```
#define LOG_SCIENTIFIC(logger, sev) (BOOST_LOG_SEV(logger, sev) << std::scientific)
```

Which can just be used as a drop-in replacement for `BOOST_LOG_SEV` which formats numbers as scientific. However, it's probably a pain to go through your code and replace every logging operation with a new custom macro. Instead of defining your own macro, you can also redefine `BOOST_LOG_SEV` to behave how you want. `boost/log/sources/severity_feature.hpp` defines `BOOST_LOG_SEV` as follows:

```
//! An equivalent to BOOST_LOG_STREAM_SEV(logger, lvl)
#define BOOST_LOG_SEV(logger, lvl) BOOST_LOG_STREAM_SEV(logger, lvl)
```

Because `BOOST_LOG_STREAM_SEV` is still a part of the public boost API, you ought to be able to safely redefine `BOOST_LOG_SEV` like this:

```
#define BOOST_LOG_SEV(logger, lvl) (BOOST_LOG_STREAM_SEV(logger, lvl) << std::scientific)
```

So long as this is defined after you have included the boost log headers, it should do what you want. However, I would recommend using a macro with a custom name, so that it is clear to others what your code is doing.

How do I set std::ios_base flags like std::left in boost log 2.0?

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