Logging in C++: Best Practices for Beginners

Introduction: Why is logging needed in C++?

Logging is the process of recording events that occur in a program during its execution. For beginner C++ developers, it might seem sufficient to output errors to the console using std::cout. However, in real projects, proper logging is a critically important tool for debugging, monitoring, and analyzing application performance.

Without a logging system, you risk:

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• Missing rare bugs that are difficult to reproduce
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• Complicating problem diagnosis in production
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• Creating unreadable code with scattered std::cout statements
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• Losing information about the sequence of events during a crash
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In this article, we will cover best practices for logging in C++ for beginners: from choosing a library to configuring performance.

Main Libraries for Logging in C++

Why shouldn't you write your own logger?

Many beginners try to write their own logging class. This is a mistake: ready-made libraries already solve problems of performance, thread safety, file rotation, and flexible formatting. Let's look at two popular options.

1. spdlog — a fast and modern choice

spdlog is a header-only library (no compilation required) that is considered one of the fastest in C++. It supports asynchronous logging, many output formats (JSON, percentages, console colors), and simple configuration.

Example of basic usage:

#include <spdlog/spdlog.h>\n#include <spdlog/sinks/basic_file_sink.h>\n\nint main() {\n    // Create a logger that writes to a file\n    auto logger = spdlog::basic_logger_mt("file_logger", "logs/app.log");\n    spdlog::set_default_logger(logger);\n    \n    // Logging levels\n    spdlog::info("Application started");\n    spdlog::warn("Low memory: {}%", 15);\n    spdlog::error("Database connection error");\n    \n    // Logging with context\n    spdlog::debug("User {} performed action {}", "admin", 42);\n    \n    return 0;\n}

2. Boost.Log — for enterprise projects

If you already use Boost in your project, Boost.Log is an excellent choice. It provides maximum flexibility: filtering by levels, multiple sinks (file, console, syslog), and support for custom attributes.

Configuration example:

#include <boost/log/trivial.hpp>\n#include <boost/log/utility/setup/file.hpp>\n\nnamespace logging = boost::log;\n\nint main() {\n    // Add a file sink\n    logging::add_file_log("logs/boost.log");\n    \n    BOOST_LOG_TRIVIAL(trace) << "Trace message";\n    BOOST_LOG_TRIVIAL(info) << "Informational message";\n    BOOST_LOG_TRIVIAL(error) << "Critical error";\n    \n    return 0;\n}

Tip for beginners: Start with spdlog — it's easier to install (just copy the header files) and has excellent documentation.

Logging Levels: When to Use What

Proper use of levels is the foundation of a readable log. In C++, the following levels are accepted (from most detailed to most critical):

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• TRACE — extremely detailed tracing (function entry/exit, variable values). Use only during debugging.
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• DEBUG — debugging information that helps the developer (object state, intermediate calculation results).
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• INFO — important application events (startup, shutdown, successful request processing).
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• WARN — potential problems that do not disrupt operation (low memory, deprecated API).
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• ERROR — errors that require intervention, but the application