Logging in C++: Best Practices for Beginners

Logging in C++ Applications: Best Practices for Beginners

Logging is the process of recording events that occur during program execution. For a beginner C++ developer, knowing how to properly organize logging is not just "good form," but a critically important skill. It helps debug code, track errors in production, and analyze system behavior. In this article, we will cover best practices for logging in C++, from the simplest methods to using modern libraries, with concrete code examples.

Why is simply using std::cout a bad practice?

Many beginners start by outputting debug messages via std::cout or printf. It's fast and simple, but this approach has serious drawbacks:

• Lack of severity levels. You cannot separate error messages from informational notifications.
• Difficulty filtering. In production, you don't want to see tons of debug messages, but during debugging you need them.
• No log rotation. The log file will grow indefinitely until it fills the entire disk.
• Multithreading issues. Output from different threads can get mixed up.

Instead, you should use specialized tools. Let's look at three main approaches: from simple to complex.

1. Simple macro wrapper for beginners

If you are writing a small educational program or don't want to include third-party libraries, you can create a simple macro wrapper. This is already better than bare cout.

#include <iostream>#include <fstream>#include <ctime>#include <string>

enum LogLevel {    DEBUG,    INFO,    WARNING,    ERROR};

std::string getCurrentTime() {    std::time_t now = std::time(nullptr);    char buf[20];    std::strftime(buf, sizeof(buf), "%Y-%m-%d %H:%M:%S", std::localtime(&now));    return std::string(buf);}

#define LOG(level, msg) \    do { \        std::ofstream logFile("app.log", std::ios::app); \        logFile << "[" << getCurrentTime() << "] " \                << "[" << #level << "] " \                << msg << std::endl; \    } while(0)

int main() {    LOG(INFO, "Program started");    int x = 42;    LOG(DEBUG, "Value of x: " << x);    // ...    LOG(ERROR, "Division by zero error occurred");    return 0;}

Pros: simplicity, no external dependencies required.

Cons: no rotation, slow performance (opening/closing file for each message), threading issues.

2. Using the spdlog library (recommended for beginners)

spdlog is the most popular logging library in C++ (over 23,000 stars on GitHub). It is very fast, simple to use, and header-only.

Installation: simply download the files from the repository or use vcpkg/conan.

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

int main() {    // Create a console logger with colored output    auto console = spdlog::stdout_color_mt("console");        // Create a file logger    auto file_logger = spdlog::basic_logger_mt("file_logger", "logs/app.log");        // Set the logging level    spdlog::set_level(spdlog::level::debug); // Log everything from DEBUG and above        // Examples of messages at different levels    console->trace("This is a trace message (lowest level)");    console->debug("Debug message: variable x = {}", 42);    console->info("Program started successfully");    console->warn("Wa