Qt Logger - Advanced Qt logging library

A simple yet powerful logging solution for the Qt Framework. This project is designed to provide developers with an intuitive and configurable logging system for Qt-based applications. QtLogger features a customizable pipeline for processing log messages through the qInstallMessageHandler() function, allowing for flexible handling and output of logs.

Pretty output

Quick start

Just copy qtlogger.h to your project directory and use the global gQtLogger object for configuration:

#include "qtlogger.h"

int main(int argc, char *argv[])
{
    QCoreApplication app(argc, argv);
    
    gQtLogger.configure();  // That's it!
    
    qDebug() << "It just works!";
    
    return app.exec();
}

Key Features

Zero code changes — works with existing qDebug(), qInfo(), qWarning(), qCritical(), qFatal()
One-line configuration: gQtLogger.configure()
Console output with optional colored output
Rotating logs with size-based, daily, and startup rotation + gzip compression
Platform-native sinks: Android logcat, macOS/iOS os_log, Linux syslog/systemd journal, Windows debugger
Network logging: HTTP endpoints for remote logging
Category-based and regex filtering for fine-grained control
Duplicate suppression to prevent log spam
Pattern formatter with rich placeholder support (time formats, fixed-width fields, conditional blocks)
JSON formatter for structured logging and log aggregation
Sentry integration for error tracking with built-in formatter and utilities
Chainable fluent API for elegant configuration
Custom attributes to enrich messages with metadata
Thread-safe concurrent logging from multiple threads
Asynchronous logging with optional dedicated thread for non-blocking I/O
Cross-platform: Linux, Windows, macOS, iOS, Android — Qt 5.9 to Qt 6.x

Integration

There are multiple ways to integrate QtLogger into your project:

Option 1: Header-Only (Simplest)

Just copy qtlogger.h to your project and include it:

#include "qtlogger.h"

This is the simplest approach - no build configuration needed.

Option 2: CMake

Link against the QtLogger library in your CMakeLists.txt:

# Add QtLogger subdirectory
add_subdirectory(path/to/qtlogger)

# Link your target
target_link_libraries(your_target PRIVATE qtlogger)

Option 3: qmake

Include the QtLogger .pri file in your .pro file:

# In your project's .pro file
include(path/to/qtlogger/qtlogger_link.pri)

More examples

Formatted logging with file rotation

This example demonstrates how to set up logging with human-readable colored output to the console (stderr) and automatic file rotation. The configure() method creates a rotating log file that compresses old logs when they exceed the specified size limit.

#include "qtlogger.h"

int main(int argc, char *argv[])
{
    QCoreApplication app(argc, argv);
    
    gQtLogger.configure("app.log", 1024 * 1024, 5,   // Max 5 files of 1 MB each
                        QtLogger::RotatingFileSink::Compression);
    
    qDebug() << "It just works!";
    
    return app.exec();
}

Advanced configuration

For more complex scenarios, you can create multiple pipelines with different filters, formatters, and sinks. Each pipeline processes log messages independently, allowing you to route different types of logs to different destinations with specific formatting.

#include "qtlogger.h"

int main(int argc, char *argv[])
{
    QCoreApplication app(argc, argv);

    // Configure with multiple pipelines
    gQtLogger
        .moveToOwnThread()                 // Asynchronous logging
        .addSeqNumber()
        .pipeline()
            .filterLevel(QtWarningMsg)     // Only warnings and above
            .filterDuplicate()
            .formatPretty()
            .sendToStdErr(true)            // Colored output
        .end()
        .pipeline()
            .format("%{time} [%{category}] %{type}: %{message}")
            .sendToFile("app.log", 1024 * 1024, 5,  // Rotating logs (1MB, 5 files)
                        QtLogger::RotatingFileSink::RotationOnStartup
                        | QtLogger::RotatingFileSink::RotationDaily
                        | QtLogger::RotatingFileSink::Compression)
        .end()
        .pipeline()
            .addAppInfo()
            .addHostInfo()
            .filter("^(?!.*password:).*$")  // Filter out sensitive data via Regex
            .formatToJson()
            .sendToHttp(QUrl("https://logs.example.com"))
        .end();

    // In advanced configuration mode, you must call this method explicitly
    gQtLogger.installMessageHandler();

    qDebug() << "Application started";
    qWarning() << "This is a warning";

    return app.exec();
}

Sentry Integration

Send warnings and errors to Sentry for error tracking. QtLogger provides a built-in SentryFormatter and utility functions for easy integration.

#include "qtlogger.h"

int main(int argc, char *argv[])
{
    QCoreApplication app(argc, argv);
    app.setApplicationName("MyApp");
    app.setApplicationVersion("1.0.0");

    // Check required environment variables
    // Set SENTRY_DSN or (SENTRY_HOST + SENTRY_PROJECT_ID + SENTRY_PUBLIC_KEY)
    if (!QtLogger::checkSentryEnv()) {
        qWarning() << "Sentry environment variables not set";
        return 1;
    }

    gQtLogger
        .moveToOwnThread()  // Async logging for non-blocking HTTP requests

        // Console output for local debugging
        .pipeline()
            .formatPretty(true)
            .sendToStdErr()
        .end()

        // Send warnings and errors to Sentry
        .pipeline()
            .addAppInfo()               // Add app name, version
            .addSysInfo()               // Add OS, kernel, CPU info
            .addHostInfo()              // Add hostname
            .filterLevel(QtWarningMsg)  // Only warnings and above
            .filterDuplicate()          // Prevent spam
            .formatToSentry()
            .sendToHttp(QtLogger::sentryUrl(), QtLogger::sentryHeaders())
        .end();

    gQtLogger.installMessageHandler();

    qWarning() << "This warning is sent to Sentry";
    qCritical() << "This error is sent to Sentry";

    return app.exec();
}

Environment variables:

SENTRY_DSN — Full Sentry DSN URL (e.g., https://key@o123.ingest.sentry.io/123)
Or use individual variables: SENTRY_HOST, SENTRY_PROJECT_ID, SENTRY_PUBLIC_KEY

Configuration from file

You can configure the logger at runtime using an INI configuration file. This approach allows you to change logging behavior without recompiling your application.

// Load configuration from INI file
gQtLogger.configureFromIniFile("config.ini");

Example config.ini:

[logger]
filter_rules = "*.debug=false"
message_pattern = "%{time} [%{category}] %{type}: %{message}"
stdout_color = true
path = "app.log"
max_file_size = 1048576
max_file_count = 5
rotate_on_startup = true
rotate_daily = false
compress_old_files = false
async = true

Comparison with Other Libraries

| Feature | QtLogger | Log4Qt | QsLog | spdlog | |---------|----------|--------|-------|--------| | Qt Integration | Native (qDebug(), qInfo(), etc.) | Own API | Own API | Own API | | Header-only option | ✅ | ❌ | ❌ | ✅ | | Zero code changes | ✅ | ❌ | ❌ | ❌ | | Colored console output | ✅ | ❌ | ✅ | ✅ | | File rotation | ✅ (size/daily/startup) | ✅ (size) | ✅ (size) | ✅ (size/daily) | | Gzip compression | ✅ | ❌ | ❌ | ❌ | | Async logging | ✅ | ❌ | ✅ | ✅ | | JSON formatter | ✅ | ❌ | ❌ | ✅ | | Sentry formatter | ✅ | ❌ | ❌ | ❌ | | Pattern formatter | ✅ | ✅ | ❌ | ✅ | | HTTP sink | ✅ | ❌ | ❌ | ❌ | | Android logcat | ✅ | ❌ | ❌ | ✅ | | macOS/iOS os_log | ✅ | ❌ | ❌ | ❌ | | Linux syslog/journald | ✅ | ✅ | ❌ | ✅ | | Duplicate suppression | ✅ | ❌ | ❌ | ❌ | | Category filtering | ✅ | ✅ | ❌ | ❌ | | Regex filtering | ✅ | ❌ | ❌ | ❌ | | Fluent API | ✅ | ❌ | ❌ | ❌ | | INI configuration | ✅ | ✅ (XML) | ❌ | ❌ | | Qt dependency | Required | Required | Required | None | | License | MIT | Apache 2.0 | BSD/MIT | MIT |

Requirements

C++17 compatible compiler: QtLogger requires a compiler with full C++17 standard support
Qt Framework: Qt 5.9 - Qt 6.x

Documentation

Full documentation is available in the docs/ directory:

Getting Started — Installation, integration options, and Hello World examples
Architecture — Pipeline concept, data flow, and handler types
Configuration Guide — Fluent API, INI file configuration, and Qt logging rules
API Reference — Complete API documentation
- Core Classes — Logger, LogMessage, utilities
- Pipelines — Pipeline, SimplePipeline, SortedPipeline
- Sinks — File, Console, Network, Syslog, and platform-specific outputs
- Formatters — Pattern, JSON, Pretty formatters with full placeholder reference
- Filters — Level, Category, RegExp, and Duplicate filters
- Attribute Handlers — Custom attributes, AppInfo, HostInfo, SeqNumber
Advanced Usage — Async logging, thread safety, cu

Qtlogger

Install / Use

README