Logging in C++: Overview of the Best Libraries and Solutions

Logging for C++: Best Solutions

Logging is one of the most important tools in a developer's arsenal. It helps track program execution, find errors, analyze performance, and collect data for debugging. The C++ language does not have a built-in logging system (unlike Java or Python), but the community and large companies have created many excellent libraries. In this article, we will look at the best solutions for logging in C++: spdlog, Boost.Log, Google glog, and fmtlog. You will learn their features, advantages, and get code examples.

Why is logging needed in C++?

In modern C++ projects, logging solves several tasks:

• Debugging: recording variable values, call stacks, object states.
• Monitoring: recording execution time of functions, I/O operations.
• Auditing: saving the history of user or system actions.
• Failure diagnostics: recording exceptions and critical errors.

A good logging library should be fast, flexible, support different log levels (debug, info, warn, error, fatal), and be able to output data to a file, console, or remote server.

1. spdlog — Fast and Modern Logger

spdlog is currently the most popular library for logging in C++. It is written in modern C++ (C++11/14/17), is header-only, and has no external dependencies except fmtlib for string formatting. Main advantages:

• High performance (asynchronous logging).
• Support for many sinks: file, console, syslog, databases.
• Flexible formatting configuration.
• Simple API.

Example of using spdlog:

#include <spdlog/spdlog.h>#include <spdlog/sinks/basic_file_sink.h>

int main() {    // Create a logger that writes to the file "logs.txt"    auto logger = spdlog::basic_logger_mt("file_logger", "logs.txt");    spdlog::set_default_logger(logger);    spdlog::set_level(spdlog::level::debug); // Logging level

    spdlog::info("Welcome to spdlog!");    spdlog::debug("Some debug message: {}", 42);    spdlog::error("Error occurred: {}", errno);

    // Asynchronous logging    spdlog::flush_on(spdlog::level::err);    return 0;}

spdlog also supports asynchronous mode, which is critical for high-load applications. Configuring asynchronicity is trivial: just call spdlog::init_thread_pool(...).

2. Boost.Log — Powerful but Heavyweight

Boost.Log is part of the Boost libraries. It is the most feature-rich solution, but it requires installing Boost and can slow down compilation. Features:

• Maximum flexibility: custom filters, formatters, sinks.
• Support for multithreading and thread safety.
• Ability to write logs to multiple destinations simultaneously (file + console + network).
• Support for log rotation by size, date, or time.

Example of Boost.Log:

#include <boost/log/trivial.hpp>#include <boost/log/expressions.hpp>#include <boost/log/utility/setup/file.hpp>

namespace logging = boost::log;

int main() {    // Configure output to a file    logging::add_file_log("sample.log");    logging::core::get()->set_filter(        logging::trivial::severity >= logging::trivial::info    );

    BOOST_LOG_TRIVIAL(trace) << "A trace severity message";    BOOST_LOG_TRIVIAL(debug) << "A debug severity message";    BOOST_LOG_TRIVIAL(error) << "An error severity message";    return 0;}

Boost.Log is a cho