Fast C++ logging library.
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 - 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
#include "spdlog/spdlog.h"
int main()
{
spdlog::info("Welcome to spdlog!");
spdlog::error("Some error message with arg: {}", 1);
spdlog::warn("Easy padding in numbers like {:08d}", 12);
spdlog::critical("Support for int: {0:d}; hex: {0:x}; oct: {0:o}; bin: {0:b}", 42);
spdlog::info("Support for floats {:03.2f}", 1.23456);
spdlog::info("Positional args are {1} {0}..", "too", "supported");
spdlog::info("{:<30}", "left aligned");
spdlog::set_level(spdlog::level::debug); // Set global log level to debug
spdlog::debug("This message should be displayed..");
// change log pattern
spdlog::set_pattern("[%H:%M:%S %z] [%n] [%^---%L---%$] [thread %t] %v");
// Compile time log levels
// Note that this does not change the current log level, it will only
// remove (depending on SPDLOG_ACTIVE_LEVEL) the call on the release code.
SPDLOG_TRACE("Some trace message with param {}", 42);
SPDLOG_DEBUG("Some debug message");
}
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
// many types of std::container<char> types can be used.
// ranges are supported too.
// format flags:
// {:X} - print in uppercase.
// {:s} - don't separate each byte with space.
// {:p} - don't print the position on each line start.
// {:n} - don't split the output into lines.
// {:a} - show ASCII if :n is not set.
#include "spdlog/fmt/bin_to_hex.h"
void binary_example()
{
auto console = spdlog::get("console");
std::array<char, 80> buf;
console->info("Binary example: {}", spdlog::to_hex(buf));
console->info("Another binary example:{:n}", spdlog::to_hex(std::begin(buf), std::begin(buf) + 10));
// more examples:
// logger->info("uppercase: {:X}", spdlog::to_hex(buf));
// logger->info("uppercase, no delimiters: {:Xs}", spdlog::to_hex(buf));
// logger->info("uppercase, no delimiters, no position info: {:Xsp}", spdlog::to_hex(buf));
}
Logger with multi sinks - each with a different format and log level
// create a logger with 2 targets, with different log levels and formats.
// The console will show only warnings or errors, while the file will log all.
void multi_sink_example()
{
auto console_sink = std::make_shared<spdlog::sinks::stdout_color_sink_mt>();
console_sink->set_level(spdlog::level::warn);
console_sink->set_pattern("[multi_sink_example] [%^%l%$] %v");
auto file_sink = std::make_shared<spdlog::sinks::basic_file_sink_mt>("logs/multisink.txt", true);
file_sink->set_level(spdlog::level::trace);
spdlog::logger logger("multi_sink", {console_sink, file_sink});
logger.set_level(spdlog::level::debug);
logger.warn("this should appear in both console and file");
logger.info("this message should not appear in the console, only in the file");
}
User-defined callbacks about log events
// create a logger with a lambda function callback, the callback will be called
// each time something is logged to the logger
void callback_example()
{
auto callback_sink = std::make_shared<spdlog::sinks::callback_sink_mt>([](const spdlog::details::log_msg &msg) {
// for example you can be notified by sending an email to yourself
});
callback_sink->set_level(spdlog::level::err);
auto console_sink = std::make_shared<spdlog::sinks::stdout_color_sink_mt>();
spdlog::logger logger("custom_callback_logger", {console_sink, callback_sink});
logger.info("some info log");
logger.error("critical issue"); // will notify you
}
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
#include "spdlog/async.h"
#include "spdlog/sinks/stdout_color_sinks.h"
#include "spdlog/sinks/rotating_file_sink.h"
void multi_sink_example2()
{
spdlog::init_thread_pool(8192, 1);
auto stdout_sink = std::make_shared<spdlog::sinks::stdout_color_sink_mt >();
auto rotating_sink = std::make_shared<spdlog::sinks::rotating_file_sink_mt>("mylog.txt", 1024*1024*10, 3);
std::vector<spdlog::sink_ptr> sinks {stdout_sink, rotating_sink};
auto logger = std::make_shared<spdlog::async_logger>("loggername", sinks.begin(), sinks.end(), spdlog::thread_pool(), spdlog::async_overflow_policy::block);
spdlog::register_logger(logger);
}
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
// Log patterns can contain custom flags.
// the following example will add new flag '%*' - which will be bound to a <my_formatter_flag> instance.
#include "spdlog/pattern_formatter.h"
class my_formatter_flag : public spdlog::custom_flag_formatter
{
public:
void format(const spdlog::details::log_msg &, const std::tm &, spdlog::memory_buf_t &dest) override
{
std::string some_txt = "custom-flag";
dest.append(some_txt.data(), some_txt.data() + some_txt.size());
}
std::unique_ptr<custom_flag_formatter> clone() const override
{
return spdlog::details::make_unique<my_formatter_flag>();
}
};
void custom_flags_example()
{
auto formatter = std::make_unique<spdlog::pattern_formatter>();
formatter->add_flag<my_formatter_flag>('*').set_pattern("[%n] [%*] [%^%l%$] %v");
spdlog::set_formatter(std::move(formatter));
}
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 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
// You can get callbacks from spdlog before/after a log file has been opened or closed.
// This is useful for cleanup procedures or for adding something to the start/end of the log file.
void file_events_example()
{
// pass the spdlog::file_event_handlers to file sinks for open/close log file notifications
spdlog::file_event_handlers handlers;
handlers.before_open = [](spdlog::filename_t filename) { spdlog::info("Before opening {}", filename); };
handlers.after_open = [](spdlog::filename_t filename, std::FILE *fstream) { fputs("After opening\n", fstream); };
handlers.before_close = [](spdlog::filename_t filename, std::FILE *fstream) { fputs("Before closing\n", fstream); };
handlers.after_close = [](spdlog::filename_t filename) { spdlog::info("After closing {}", filename); };
auto my_logger = spdlog::basic_logger_st("some_logger", "logs/events-sample.txt", true, 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
[info] **************************************************************
[info] Single thread, 1,000,000 iterations
[info] **************************************************************
[info] basic_st Elapsed: 0.17 secs 5,777,626/sec
[info] rotating_st Elapsed: 0.18 secs 5,475,894/sec
[info] daily_st Elapsed: 0.20 secs 5,062,659/sec
[info] empty_logger Elapsed: 0.07 secs 14,127,300/sec
[info] **************************************************************
[info] C-string (400 bytes). Single thread, 1,000,000 iterations
[info] **************************************************************
[info] basic_st Elapsed: 0.41 secs 2,412,483/sec
[info] rotating_st Elapsed: 0.72 secs 1,389,196/sec
[info] daily_st Elapsed: 0.42 secs 2,393,298/sec
[info] null_st Elapsed: 0.04 secs 27,446,957/sec
[info] **************************************************************
[info] 10 threads, competing over the same logger object, 1,000,000 iterations
[info] **************************************************************
[info] basic_mt Elapsed: 0.60 secs 1,659,613/sec
[info] rotating_mt Elapsed: 0.62 secs 1,612,493/sec
[info] daily_mt Elapsed: 0.61 secs 1,638,305/sec
[info] null_mt Elapsed: 0.16 secs 6,272,758/sec
Asynchronous mode
[info] -------------------------------------------------
[info] Messages : 1,000,000
[info] Threads : 10
[info] Queue : 8,192 slots
[info] Queue memory : 8,192 x 272 = 2,176 KB
[info] -------------------------------------------------
[info]
[info] *********************************
[info] Queue Overflow Policy: block
[info] *********************************
[info] Elapsed: 1.70784 secs 585,535/sec
[info] Elapsed: 1.69805 secs 588,910/sec
[info] Elapsed: 1.7026 secs 587,337/sec
[info]
[info] *********************************
[info] Queue Overflow Policy: overrun
[info] *********************************
[info] Elapsed: 0.372816 secs 2,682,285/sec
[info] Elapsed: 0.379758 secs 2,633,255/sec
[info] Elapsed: 0.373532 secs 2,677,147/sec
Documentation
Documentation can be found in the wiki pages.
Thanks to JetBrains for donating product licenses to help develop spdlog 