GitHub - gabime/spdlog: Fast C++ logging library. (original) (raw)

spdlog

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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

Package managers:

Features

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 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_sharedspdlog::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_sharedspdlog::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_mtspdlog::async_factory("async_file_logger", "logs/async_log.txt"); // alternatively: // auto async_file = spdlog::create_asyncspdlog::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_sharedspdlog::sinks::rotating_file_sink_mt("mylog.txt", 1024102410, 3); std::vectorspdlog::sink_ptr sinks {stdout_sink, rotating_sink}; auto logger = std::make_sharedspdlog::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 : fmt::formatterstd::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 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_uniquespdlog::pattern_formatter(); formatter->add_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 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

// 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.

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