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


Currently Crow's Logger is not linked to the Crow application, meaning if an executable has more than one Crow application they'll be sharing any variables or classes relating to Logging.

Setting up logging level

You can set up the level at which crow displays logs by using the app's loglevel(crow::LogLevel) method.

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

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


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 CROW_LOG_<LOG LEVEL> << "Hello"; (replace<LOG LEVEL> with the actual level in all caps, so you have CROW_LOG_WARNING).


Log times are reported in GMT timezone by default. This is because HTTP requires all reported times for requests and responses to be in GMT. This can be changed by using the macro CROW_USE_LOCALTIMEZONE which will set only the log timezone to the server's local timezone.

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.
All you need is a class extending crow::ILogHandler containing the method void log(std::string, crow::LogLevel).
Once you have your custom logger, you need to set it via crow::logger::setHandler(&MyLogger);. Here's a full example:

class CustomLogger : public crow::ILogHandler {
  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::SimpleApp app;
  CROW_ROUTE(app, "/")([]() { return "Hello"; });;