Fast C++ logging library.
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gabime Merge pull request #945 from cneumann/fix-external-fmt
Fix handling of external fmt lib
Latest commit 0955ea5 Dec 17, 2018


Very fast, header only, C++ logging library. Build Status  Build status


Just copy the headers:

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

Or use your favorite package manager:

  • Ubuntu: apt-get install libspdlog-dev
  • Homebrew: brew install spdlog
  • FreeBSD: cd /usr/ports/devel/spdlog/ && make install clean
  • Fedora: yum install spdlog
  • Gentoo: emerge dev-libs/spdlog
  • Arch Linux: yaourt -S spdlog-git
  • vcpkg: vcpkg install spdlog


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


  • Very fast (see benchmarks below).
  • Headers only, just copy and use.
  • Feature rich formatting, using the excellent fmt library.
  • Fast asynchronous mode (optional)
  • Custom formatting.
  • Multi/Single threaded loggers.
  • Various log targets:
    • Rotating log files.
    • Daily log files.
    • Console logging (colors supported).
    • syslog.
    • Windows debugger (OutputDebugString(..))
    • Easily extendable with custom log targets (just implement a single function in the sink interface).
  • Severity based filtering - threshold levels can be modified in runtime as well as in compile time.
  • Binary data logging.


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

Synchronous mode

Single thread, 1,000,000 iterations
basic_st...             Elapsed: 0.181652       5,505,042/sec
rotating_st...          Elapsed: 0.181781       5,501,117/sec
daily_st...             Elapsed: 0.187595       5,330,630/sec
null_st...              Elapsed: 0.0504704      19,813,602/sec
10 threads sharing same logger, 1,000,000 iterations
basic_mt...             Elapsed: 0.616035       1,623,284/sec
rotating_mt...          Elapsed: 0.620344       1,612,008/sec
daily_mt...             Elapsed: 0.648353       1,542,369/sec
null_mt...              Elapsed: 0.151972       6,580,166/sec

Asynchronous mode

10 threads sharing same logger, 1,000,000 iterations 
async...                Elapsed: 0.350066       2,856,606/sec
async...                Elapsed: 0.314865       3,175,960/sec
async...                Elapsed: 0.349851       2,858,358/sec

Usage samples

#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");
    console->info("Welcome to spdlog!");
    console->error("Some error message with arg: {}", 1);

    auto err_logger = spdlog::stderr_color_mt("stderr");
    err_logger->error("Some error message");

    // Formatting examples
    console->warn("Easy padding in numbers like {:08d}", 12);
    console->critical("Support for int: {0:d};  hex: {0:x};  oct: {0:o}; bin: {0:b}", 42);
    console->info("Support for floats {:03.2f}", 1.23456);
    console->info("Positional args are {1} {0}..", "too", "supported");
    console->info("{:<30}", "left aligned");

    spdlog::get("console")->info("loggers can be retrieved from a global registry using the spdlog::get(logger_name)");

    // Runtime log levels
    spdlog::set_level(spdlog::level::info); // Set global log level to info
    console->debug("This message should not be displayed!");
    console->set_level(spdlog::level::trace); // Set specific logger's log level
    console->debug("This message should be displayed..");

    // Customize msg format for all loggers
    spdlog::set_pattern("[%H:%M:%S %z] [%n] [%^---%L---%$] [thread %t] %v");
    console->info("This an info message with custom format");

    // Compile time log levels
    SPDLOG_TRACE(console, "Enabled only #ifdef SPDLOG_TRACE_ON..{} ,{}", 1, 3.23);
    SPDLOG_DEBUG(console, "Enabled only #ifdef SPDLOG_DEBUG_ON.. {} ,{}", 1, 3.23);

Basic file logger

#include "spdlog/sinks/basic_file_sink.h"
void basic_logfile_example()
        auto my_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 rotating_logger = spdlog::rotating_logger_mt("some_logger_name", "logs/rotating.txt", 1048576 * 5, 3);

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 daily_logger = spdlog::daily_logger_mt("daily_logger", "logs/daily.txt", 2, 30);

Cloning loggers

// clone a logger and give it new name.
// Useful for creating subsystem loggers from some "root" logger
void clone_example()
    auto network_logger = spdlog::get("root")->clone("network");
    network_logger->info("Logging network stuff..");

Periodic flush

// periodically flush all *registered* loggers every 3 seconds:
// warning: only use if all your loggers are thread safe!

Binary logging

// log binary data as 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.

#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");"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});

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("android", tag);
    android_logger->critical("Use \"adb shell logcat\" to view this message.");


Documentation can be found in the wiki pages.