Default logger with multiple targets controlled by environment variables

[AndyDralle]

Hey there!

I have taken a look at #2444 and #79. While very much related to my issue, I don't think they solve it completely, though:

I would like to use the default_logger for logging to multiple targets, such as a file and stdout. Further, I would like to use spdlog::cfg::load_env_levels() to control the logging to these different targets. My goal is to set the log level individually using separate environment variables for each target.

Approach A (#79):
While I could create a logger with multiple sinks, each with their own log level, I can't control the level of a sink via an environment variable. This only works for loggers.

Approach B (#2444):
I don't actually know how to create a sink that forwards messages to multiple loggers.

Say I have a list of loggers: std::vector<spdlog::logger> loggers.
If I implement sink_it_ for my custom sink like this:

  void sink_it_(const spdlog::details::log_msg& message) override {
    for (auto& logger : loggers) {
      logger.sink_it_(message);
    }
  }

I skip the actual logging part. I.e., by directly sinking, I skip the logic verifying the log level, right?
I don't know how to call .log() on my loggers, given that my message is of type log_msg&.

Is there a way to achieve this?

[gabime]

Try passing the message.level and message.payload to each logger.log()

[AndyDralle]

That seems to do the trick. My sink implementation now looks like this:

  void sink_it_(const spdlog::details::log_msg& message) override {
    for (auto& logger : loggers) {
      logger->log(message.time, message.source, message.level, message.payload);
    }
  }

  void flush_() override {
    for (auto& logger : loggers) {
      logger->flush();
    }
  }

Thank you!