Using spdlog::level::off to unconditionally log a message, OK?

[N-Dekker]

I would like to replace a few print statements in an existing code base by corresponding spdlog calls. Those old print statements were unconditional (independent of any logging level), but not necessarily "critical". Is that a valid use case for spdlog::level::off? For example:

 my_logger.log(spdlog::level::off, message);

Just to be sure! 😃

[tt4g]

spdlog::level::off is used to suppress all logging. Using spdlog::level::trace will output all logs.

spdlog/include/spdlog/logger.h

Lines 300 to 304 in 927cc29

	// return true logging is enabled for the given level.
	bool should_log(level::level_enum msg_level) const
	{
	return msg_level >= level_.load(std::memory_order_relaxed);
	}

spdlog/include/spdlog/common.h

Lines 223 to 235 in 927cc29

	// Log level enum
	namespace level {
	enum level_enum : int
	{
	trace = SPDLOG_LEVEL_TRACE,
	debug = SPDLOG_LEVEL_DEBUG,
	info = SPDLOG_LEVEL_INFO,
	warn = SPDLOG_LEVEL_WARN,
	err = SPDLOG_LEVEL_ERROR,
	critical = SPDLOG_LEVEL_CRITICAL,
	off = SPDLOG_LEVEL_OFF,
	n_levels
	};

[N-Dekker]

Thanks @tt4g I did not realize before that for a message level, the value level::off suppressed automatic flushing. But I guess an explicit logger::flush() call in user code still flushes such "level::off messages", right?

[tt4g]

logger::flush() always works. Automatic flushing after log message output only is not performed.

[N-Dekker]

So I learned here that when a specific message itself has message log level off:

1. such a message is logged unconditionally, unfiltered, independent of any logger's log level
2. such a message is not flushed automatically

Has this specific behavior of logging a "level off message" already been documented? If not, do you think this could still be added, for example to the wiki?

[tt4g]

There is no documentation for spdlog::level::off as far as I know (there is a section on filtering by log level in README.md).
Since the wiki is community based and maintained, you can add an explanation when setting spdlog::level::off to the log message.

[tt4g]

Added: https://github.com/gabime/spdlog/wiki/0.-FAQ#how-to-force-log-messages-to-be-output-ignore-log-level-filter

I am not a native speaker, so please edit if there is anything that needs to be edited.