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https://github.com/gabime/spdlog

Fast C++ logging library.
https://github.com/gabime/spdlog

cpp cpp11 header-only logging spdlog

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Fast C++ logging library.

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# spdlog



 

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[![Build status](https://ci.appveyor.com/api/projects/status/d2jnxclg20vd0o50?svg=true&branch=v1.x)](https://ci.appveyor.com/project/gabime/spdlog) [![Release](https://img.shields.io/github/release/gabime/spdlog.svg)](https://github.com/gabime/spdlog/releases/latest)



Fast C++ logging library



## Install

#### Header-only version

Copy the include [folder](https://github.com/gabime/spdlog/tree/v1.x/include/spdlog) to your build tree and use a C++11 compiler.



#### Compiled version (recommended - much faster compile times)

```console

$ git clone https://github.com/gabime/spdlog.git

$ cd spdlog && mkdir build && cd build

$ cmake .. && cmake --build .

```

see example [CMakeLists.txt](https://github.com/gabime/spdlog/blob/v1.x/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](#benchmarks) below).

* Headers only or compiled

* Feature-rich formatting, using the excellent [fmt](https://github.com/fmtlib/fmt) library.

* Asynchronous mode (optional)

* [Custom](https://github.com/gabime/spdlog/wiki/3.-Custom-formatting) 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](#log-to-qt-with-nice-colors)).

  * Easily [extendable](https://github.com/gabime/spdlog/wiki/4.-Sinks#implementing-your-own-sink) 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](#backtrace-support) support - store debug messages in a ring buffer and display them later on demand.



## Usage samples



#### Basic usage

```c++

#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

```c++

#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

```c++

#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

```c++

#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

```c++



#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

```c++

// 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

```c++

// 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

```c++

// 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

```c++

// many types of std::container 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 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

```c++



// 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();

    console_sink->set_level(spdlog::level::warn);

    console_sink->set_pattern("[multi_sink_example] [%^%l%$] %v");



    auto file_sink = std::make_shared("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

```c++



// 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([](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::logger logger("custom_callback_logger", {console_sink, callback_sink});



    logger.info("some info log");

    logger.error("critical issue"); // will notify you

}

```



---

#### Asynchronous logging

```c++

#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("async_file_logger", "logs/async_log.txt");

    // alternatively:

    // auto async_file = spdlog::create_async("async_file_logger", "logs/async_log.txt");   

}



```



---

#### Asynchronous logger with multi sinks

```c++

#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();

    auto rotating_sink = std::make_shared("mylog.txt", 1024*1024*10, 3);

    std::vector sinks {stdout_sink, rotating_sink};

    auto logger = std::make_shared("loggername", sinks.begin(), sinks.end(), spdlog::thread_pool(), spdlog::async_overflow_policy::block);

    spdlog::register_logger(logger);

}

```

 

---

#### User-defined types

```c++

template<>

struct fmt::formatter : fmt::formatter

{

    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

```c++ 

// Log patterns can contain custom flags.

// the following example will add new flag '%*' - which will be bound to a  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 clone() const override

    {

        return spdlog::details::make_unique();

    }

};



void custom_flags_example()

{    

    auto formatter = std::make_unique();

    formatter->add_flag('*').set_pattern("[%n] [%*] [%^%l%$] %v");

    spdlog::set_formatter(std::move(formatter));

}



```



---

#### Custom error handler

```c++

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

```c++

#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

```c++

#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



```c++

#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:



```console

$ export SPDLOG_LEVEL=info,mylogger=trace

$ ./example

```



---

#### Log file open/close event handlers

```c++

// 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

```c++

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

```c++

#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

```c++

// 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](https://github.com/gabime/spdlog/blob/v1.x/bench/bench.cpp) 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](https://github.com/gabime/spdlog/wiki/1.-QuickStart) pages.



---



Thanks to [JetBrains](https://www.jetbrains.com/?from=spdlog) for donating product licenses to help develop **spdlog**