Crow/docs/guides/logging.md

Crow comes with a simple and easy to use logging system.<br><br>

## Setting up logging level
You can set up the level at which crow displays logs by using the app's `loglevel(crow::LogLevel)` method.<br><br>

The available log levels are as follows (please not that setting a level will also display all logs below this level):

- Debug
- Info
- Warning
- Error
- Critical
<br><br>

To set a logLevel, just use `#!cpp app.loglevel(crow::LogLevel::Warning)`, This will not show any debug or info logs. It will however still show error and critical logs.<br><br>

!!! note

    Setting the Macro `CROW_ENABLE_DEBUG` during compilation will also set the log level to `Debug` (unless otherwise set using `loglevel()`).


## Writing a log
Writing a log is as simple as `#!cpp CROW_LOG_<LOG LEVEL> << "Hello";` (replace&lt;LOG LEVEL&gt; with the actual level in all caps, so you have `CROW_LOG_WARNING`).

## Creating A custom logger
Assuming you have an existing logger or Crow's default format just doesn't work for you. Crow allows you to use a custom logger for any log made using the `CROW_LOG_<LOG LEVEL>` macro.<br>
All you need is a class extending `#!cpp crow::ILogHandler` containing the method `#!cpp void log(std::string, crow::LogLevel)`.<br>
Once you have your custom logger, you need to set it via `#!cpp crow::logger::setHandler(&MyLogger);`. Here's a full example:<br>
```cpp
class CustomLogger : public crow::ILogHandler {
 public:
  CustomLogger() {}
  void log(std::string message, crow::LogLevel /*level*/) {
    // "message" doesn't contain the timestamp and loglevel
    // prefix the default logger does and it doesn't end
    // in a newline.
    std::cerr << message << std::endl;
  }
};

int main(int argc, char** argv) {
  CustomLogger logger;
  crow::logger::setHandler(&logger);

  crow::SimpleApp app;
  CROW_ROUTE(app, "/")([]() { return "Hello"; });
  app.run();
}
```