Fast C++ logging library.





GitHub Stars



Last Commit

7d ago











Very fast, header-only/compiled, C++ logging library. Build Status  Build status Release


Header only version

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

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

see example CMakeLists.txt on how to use.


  • 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
  • vcpkg: vcpkg install spdlog
  • conan: spdlog/[>=1.4.1]
  • conda: conda install -c conda-forge spdlog
  • build2: depends: spdlog ^1.8.2


  • 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(..)).
    • Easily extendable with custom log targets.
  • Log filtering - log levels can be modified in runtime as well as in compile time.
  • Support for loading log levels from argv or from environment var.
  • Backtrace support - store debug messages in a ring buffer and display 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
    // define SPDLOG_ACTIVE_LEVEL to desired level
    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 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()
        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 5mb 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 on 2:30am
    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 in order to display debug logs only when really needed (e.g. when error happens).
// When needed, call dump_backtrace() to see them.

spdlog::enable_backtrace(32); // Store the latest 32 messages in a buffer. Older messages will be dropped.
// 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)


// 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 to 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 different format and log level

// create 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_pattern("[multi_sink_example] [%^%l%$] %v");

    auto file_sink = std::make_shared<spdlog::sinks::basic_file_sink_mt>("logs/multisink.txt", true);

    spdlog::logger logger("multi_sink", {console_sink, file_sink});
    logger.warn("this should appear in both console and file");
    logger.info("this message should not appear in the console, only in the file");

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/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);

User defined types

// user defined types logging by implementing operator<<
#include "spdlog/fmt/ostr.h" // must be included
struct my_type
    int i;
    template<typename OStream>
    friend OStream &operator<<(OStream &os, const my_type &c)
        return os << "[my_type i=" << c.i << "]";

void user_defined_example()
    spdlog::get("console")->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
    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");

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);


#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 env variable or from argv

#include "spdlog/cfg/env.h"
int main (int argc, char *argv[])
    // or from 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


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] 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] 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 can be found in the wiki pages.

Thanks to JetBrains for donating product licenses to help develop spdlog

Rate & Review

Great Documentation0
Easy to Use0
Highly Customizable0
Bleeding Edge0
Responsive Maintainers0
Poor Documentation0
Hard to Use0
Unwelcoming Community0
No reviews found
Be the first to rate


No alternatives found


No tutorials found
Add a tutorial