spdlog

spdlog

     

Fast C++ logging library

Install

Header-only version

Copy the include folder to your build tree and use a C++11 compiler.

Compiled version (recommended - much faster compile times)

$ git clone https://github.com/gabime/spdlog.git
$ cd spdlog && mkdir build && cd build
$ cmake .. && cmake --build .

see example CMakeLists.txt on how to use.

Platforms

• Linux, FreeBSD, OpenBSD, Solaris, AIX
• Windows (msvc 2013+, cygwin)
• macOS (clang 3.5+)
• Android

Package managers:

• Debian: sudo apt install libspdlog-dev
• Homebrew: brew install spdlog
• MacPorts: sudo port install spdlog
• FreeBSD: pkg install spdlog
• Fedora: dnf install spdlog
• Gentoo: emerge dev-libs/spdlog
• Arch Linux: pacman -S spdlog
• openSUSE: sudo zypper in spdlog-devel
• ALT Linux: apt-get install libspdlog-devel
• vcpkg: vcpkg install spdlog
• conan: conan install --requires=spdlog/[*]
• conda: conda install -c conda-forge spdlog
• build2: depends: spdlog ^1.8.2

Features

• Very fast (see benchmarks below).
• Headers only or compiled
• Feature-rich formatting, using the excellent fmt library.
• Asynchronous mode (optional)
• Custom formatting.
• Multi/Single threaded loggers.
• Various log targets:
  • Rotating log files.
  • Daily log files.
  • Console logging (colors supported).
  • syslog.
  • Windows event log.
  • Windows debugger (OutputDebugString(..)).
  • Log to Qt widgets (example).
  • Easily extendable with custom log targets.
• Log filtering - log levels can be modified at runtime as well as compile time.
• Support for loading log levels from argv or environment var.
• Backtrace support - store debug messages in a ring buffer and display them later on demand.

Usage samples

Basic usage

…

---

Create stdout/stderr logger object

#include "spdlog/spdlog.h"
#include "spdlog/sinks/stdout_color_sinks.h"
void stdout_example()
{
    // create a color multi-threaded logger
    auto console = spdlog::stdout_color_mt("console");    
    auto err_logger = spdlog::stderr_color_mt("stderr");    
    spdlog::get("console")->info("loggers can be retrieved from a global registry using the spdlog::get(logger_name)");
}

---

Basic file logger

#include "spdlog/sinks/basic_file_sink.h"
void basic_logfile_example()
{
    try 
    {
        auto logger = spdlog::basic_logger_mt("basic_logger", "logs/basic-log.txt");
    }
    catch (const spdlog::spdlog_ex &ex)
    {
        std::cout << "Log init failed: " << ex.what() << std::endl;
    }
}

---

Rotating files

#include "spdlog/sinks/rotating_file_sink.h"
void rotating_example()
{
    // Create a file rotating logger with 5 MB size max and 3 rotated files
    auto max_size = 1048576 * 5;
    auto max_files = 3;
    auto logger = spdlog::rotating_logger_mt("some_logger_name", "logs/rotating.txt", max_size, max_files);
}

---

Daily files

#include "spdlog/sinks/daily_file_sink.h"
void daily_example()
{
    // Create a daily logger - a new file is created every day at 2:30 am
    auto logger = spdlog::daily_logger_mt("daily_logger", "logs/daily.txt", 2, 30);
}

---

Backtrace support

// Debug messages can be stored in a ring buffer instead of being logged immediately.
// This is useful to display debug logs only when needed (e.g. when an error happens).
// When needed, call dump_backtrace() to dump them to your log.

spdlog::enable_backtrace(32); // Store the latest 32 messages in a buffer. 
// or my_logger->enable_backtrace(32)..
for(int i = 0; i < 100; i++)
{
  spdlog::debug("Backtrace message {}", i); // not logged yet..
}
// e.g. if some error happened:
spdlog::dump_backtrace(); // log them now! show the last 32 messages
// or my_logger->dump_backtrace(32)..

---

Periodic flush

// periodically flush all *registered* loggers every 3 seconds:
// warning: only use if all your loggers are thread-safe ("_mt" loggers)
spdlog::flush_every(std::chrono::seconds(3));

---

Stopwatch

// Stopwatch support for spdlog
#include "spdlog/stopwatch.h"
void stopwatch_example()
{
    spdlog::stopwatch sw;    
    spdlog::debug("Elapsed {}", sw);
    spdlog::debug("Elapsed {:.3}", sw);       
}

---

Log binary data in hex

…

---

Logger with multi sinks - each with a different format and log level

…

---

Register several loggers - change global level

…

---

User-defined callbacks about log events

…

---

Asynchronous logging

#include "spdlog/async.h"
#include "spdlog/sinks/basic_file_sink.h"
void async_example()
{
    // default thread pool settings can be modified *before* creating the async logger:
    // spdlog::init_thread_pool(8192, 1); // queue with 8k items and 1 backing thread.
    auto async_file = spdlog::basic_logger_mt<spdlog::async_factory>("async_file_logger", "logs/async_log.txt");
    // alternatively:
    // auto async_file = spdlog::create_async<spdlog::sinks::basic_file_sink_mt>("async_file_logger", "logs/async_log.txt");   
}

---

Asynchronous logger with multi sinks

…

---

User-defined types

template<>
struct fmt::formatter<my_type> : fmt::formatter<std::string>
{
    auto format(my_type my, format_context &ctx) const -> decltype(ctx.out())
    {
        return fmt::format_to(ctx.out(), "[my_type i={}]", my.i);
    }
};

void user_defined_example()
{
    spdlog::info("user defined type: {}", my_type(14));
}

---

User-defined flags in the log pattern

…

---

Custom error handler

void err_handler_example()
{
    // can be set globally or per logger(logger->set_error_handler(..))
    spdlog::set_error_handler([](const std::string &msg) { spdlog::get("console")->error("*** LOGGER ERROR ***: {}", msg); });
    spdlog::get("console")->info("some invalid message to trigger an error {}{}{}{}", 3);
}

---

syslog

#include "spdlog/sinks/syslog_sink.h"
void syslog_example()
{
    std::string ident = "spdlog-example";
    auto syslog_logger = spdlog::syslog_logger_mt("syslog", ident, LOG_PID);
    syslog_logger->warn("This is warning that will end up in syslog.");
}

---

Android example

#include "spdlog/sinks/android_sink.h"
void android_example()
{
    std::string tag = "spdlog-android";
    auto android_logger = spdlog::android_logger_mt("android", tag);
    android_logger->critical("Use \"adb shell logcat\" to view this message.");
}

---

Load log levels from the env variable or argv

#include "spdlog/cfg/env.h"
int main (int argc, char *argv[])
{
    spdlog::cfg::load_env_levels();
    // or specify the env variable name:
    // MYAPP_LEVEL=info,mylogger=trace && ./example
    // spdlog::cfg::load_env_levels("MYAPP_LEVEL");
    // or from the command line:
    // ./example SPDLOG_LEVEL=info,mylogger=trace
    // #include "spdlog/cfg/argv.h" // for loading levels from argv
    // spdlog::cfg::load_argv_levels(argc, argv);
}

So then you can:

$ export SPDLOG_LEVEL=info,mylogger=trace
$ ./example

---

Log file open/close event handlers

…

---

Replace the Default Logger

void replace_default_logger_example()
{
    auto new_logger = spdlog::basic_logger_mt("new_default_logger", "logs/new-default-log.txt", true);
    spdlog::set_default_logger(new_logger);
    spdlog::info("new logger log message");
}

---

Log to Qt with nice colors

#include "spdlog/spdlog.h"
#include "spdlog/sinks/qt_sinks.h"
MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent)
{
    setMinimumSize(640, 480);
    auto log_widget = new QTextEdit(this);
    setCentralWidget(log_widget);
    int max_lines = 500; // keep the text widget to max 500 lines. remove old lines if needed.
    auto logger = spdlog::qt_color_logger_mt("qt_logger", log_widget, max_lines);
    logger->info("Some info message");
}

---

Mapped Diagnostic Context

// Mapped Diagnostic Context (MDC) is a map that stores key-value pairs (string values) in thread local storage.
// Each thread maintains its own MDC, which loggers use to append diagnostic information to log outputs.
// Note: it is not supported in asynchronous mode due to its reliance on thread-local storage.
#include "spdlog/mdc.h"
void mdc_example()
{
    spdlog::mdc::put("key1", "value1");
    spdlog::mdc::put("key2", "value2");
    // if not using the default format, use the %& formatter to print mdc data
    // spdlog::set_pattern("[%H:%M:%S %z] [%^%L%$] [%&] %v");
}

---

Benchmarks

Below are some benchmarks done in Ubuntu 64 bit, Intel i7-4770 CPU @ 3.40GHz

Synchronous mode

…

Asynchronous mode

…

Documentation

Documentation can be found in the wiki pages.

---

Powered by