Logger

Table of Contents

• Basic Usage
• Convert a Log Level to a String

How to use a custom logger with a MongoDB C++ Driver instance.

Basic Usage

class example_logger : public mongocxx::logger {
   private:
    int* counter_ptr;
 
   public:
    explicit example_logger(int* ptr) : counter_ptr(ptr) {}
 
    void operator()(mongocxx::log_level level,
                    bsoncxx::stdx::string_view domain,
                    bsoncxx::stdx::string_view message) noexcept override {
        EXPECT(level == mongocxx::log_level::k_info);
        EXPECT(domain == "mongocxx");
        EXPECT(message == "libmongoc logging callback enabled");
 
        *counter_ptr += 1;
    }
};
 
void example() {
    int counter = 0;
 
    // Use `std::make_unique` with C++14 or newer.
    auto logger = std::unique_ptr<mongocxx::logger>(new example_logger{&counter});
 
    // Emit the informational mongocxx log message: "libmongoc logging callback enabled".
    mongocxx::instance instance{std::move(logger)};
 
    EXPECT(counter == 1);
}

Convert a Log Level to a String

void example() {
    bsoncxx::stdx::string_view error = mongocxx::to_string(mongocxx::log_level::k_error);
    bsoncxx::stdx::string_view critical = mongocxx::to_string(mongocxx::log_level::k_critical);
    bsoncxx::stdx::string_view warning = mongocxx::to_string(mongocxx::log_level::k_warning);
    bsoncxx::stdx::string_view message = mongocxx::to_string(mongocxx::log_level::k_message);
    bsoncxx::stdx::string_view info = mongocxx::to_string(mongocxx::log_level::k_info);
    bsoncxx::stdx::string_view debug = mongocxx::to_string(mongocxx::log_level::k_debug);
    bsoncxx::stdx::string_view trace = mongocxx::to_string(mongocxx::log_level::k_trace);
 
    EXPECT(error == "error");
    EXPECT(critical == "critical");
    EXPECT(warning == "warning");
    EXPECT(message == "message");
    EXPECT(info == "info");
    EXPECT(debug == "debug");
    EXPECT(trace == "trace");
}