Qt使用spdlog日志

來源：微信公眾號「編程學習基地」

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目錄

• spdlog日志
  • 創建日志
    • 創建一個支持多線程的日志
    • 輸出打印到Concole
  • 日志等級
    • 設置日志等級
  • 輸出格式
    • 設置輸出格式
  • 關閉日志
  • 源碼閱讀
  • 參考文獻

spdlog日志

spdlog是一個開源的、快速的、僅有頭文件的C++11 日志庫，code地址在 https://github.com/gabime/spdlog 目前最新的發布版本為Version 1.8.0。它提供了向流、標准輸出、文件、系統日志、調試器等目標輸出日志的能力。它支持的平台包括Windows、Linux、Mac、Android。

spdlog只要包含頭文件即可使用，簡單方便，下載源碼之后找到include目錄，將include目錄下的spdlog復制到你需要打印日志的項目下，然后導入頭文件

#include "spdlog/spdlog.h"
#include "spdlog/sinks/rotating_file_sink.h"

創建日志

basic log

不帶滾動，日志文件會一直被寫入，不斷變大。

// Create basic file logger (not rotated)
auto my_logger = spd::basic_logger_mt("basic_logger", "logs/basic-log.txt");
my_logger->info("Some log message");

創建一個支持多線程的日志

rotating log

滾動日志，當日志文件超出規定大小時，會刪除當前日志文件中所有內容，重新開始寫入。

從函數聲明可以看出，參數max_file_size 規定了文件的最大值，文件內容超過此值就會清空。

rotating_logger_mt(const std::string& logger_name, const filename_t& filename, size_t max_file_size, size_t max_files)

參數max_files 規定了滾動文件的個數。當logger_name存滿時，將其名稱更改為logger_name.1，再新建一個logger_name文件來存儲新的日志。再次存滿時，把logger_name.1改名為logger_name.2，logger_name改名為logger_name.1，新建一個logger_name來存放新的日志。max_files 數量為幾，就可以有幾個logger_name文件用來滾動。

示例：

size_t max_size = 1024 * 10;
std::string basename = "testLog.log";
std::shared_ptr<spdlog::logger> file_logger;  //日志的文件指針
file_logger = spdlog::rotating_logger_mt("2232", basename, max_size, 0);

日志保存在工作目錄下的testLog.log里面

輸出打印到Concole

spdlog::set_pattern("%+ [thread %t]");	//設置輸出格式直接打印
spdlog::trace("This message shold not be displayed!");
spdlog::debug("This message shold not be displayed!");

控制台帶顏色輸出

日志等級

enum level_enum
{
    trace = SPDLOG_LEVEL_TRACE,
    debug = SPDLOG_LEVEL_DEBUG,
    info = SPDLOG_LEVEL_INFO,
    warn = SPDLOG_LEVEL_WARN,
    err = SPDLOG_LEVEL_ERROR,
    critical = SPDLOG_LEVEL_CRITICAL,
    off = SPDLOG_LEVEL_OFF,
};

設置日志等級

spdlog::set_level(spdlog::level::info); // Set global log level to debug

設置日志等級之后可以打印的日志等級最高位info，也就是debug和trace不打印

    spdlog::set_pattern("%+ [thread %t]");
	spdlog::set_level(spdlog::level::info); // Set global log level to debug
    spdlog::trace("This message shold not be displayed!");
    spdlog::debug("This message shold not be displayed!");

    spdlog::info("This message shold be displayed..");
    spdlog::critical("This message shold be displayed..");


    spdlog::set_level(spdlog::level::debug); // Set global log level to debug
    spdlog::debug("This message shold be displayed..");
    spdlog::critical("This message shold be displayed..");

打印結果：

[2020-09-20 00:24:29.160] [info] This message shold be displayed.. [thread 12932]
[2020-09-20 00:24:29.162] [critical] This message shold be displayed.. [thread 12932]
[2020-09-20 00:24:29.162] [debug] This message shold be displayed.. [thread 12932]
[2020-09-20 00:24:29.162] [critical] This message shold be displayed.. [thread 12932]

輸出格式

參考：https://github.com/gabime/spdlog/wiki/3.-Custom-formatting

Pattern flags are in the form of %flag and resembles the strftime function:

flag	meaning	example
%v	The actual text to log	"some user text"
%t	Thread id	"1232"
%P	Process id	"3456"
%n	Logger's name	"some logger name"
%l	The log level of the message	"debug", "info", etc
%L	Short log level of the message	"D", "I", etc
%a	Abbreviated weekday name	"Thu"
%A	Full weekday name	"Thursday"
%b	Abbreviated month name	"Aug"
%B	Full month name	"August"
%c	Date and time representation	"Thu Aug 23 15:35:46 2014"
%C	Year in 2 digits	"14"
%Y	Year in 4 digits	"2014"
%D or %x	Short MM/DD/YY date	"08/23/14"
%m	Month 01-12	"11"
%d	Day of month 01-31	"29"
%H	Hours in 24 format 00-23	"23"
%I	Hours in 12 format 01-12	"11"
%M	Minutes 00-59	"59"
%S	Seconds 00-59	"58"
%e	Millisecond part of the current second 000-999	"678"
%f	Microsecond part of the current second 000000-999999	"056789"
%F	Nanosecond part of the current second 000000000-999999999	"256789123"
%p	AM/PM	"AM"
%r	12 hour clock	"02:55:02 pm"
%R	24-hour HH:MM time, equivalent to %H:%M	"23:55"
%T or %X	ISO 8601 time format (HH:MM:SS), equivalent to %H:%M:%S	"23:55:59"
%z	ISO 8601 offset from UTC in timezone ([+/-]HH:MM)	"+02:00"
%E	Seconds since the epoch	"1528834770"
%%	The % sign	"%"
%+	spdlog's default format	"[2014-10-31 23:46:59.678] [mylogger] [info] Some message"
%^	start color range (can be used only once)	"[mylogger] [info(green)] Some message"
%$	end color range (for example %[1]%$ %v) (can be used only once)	[+++] Some message
%@	Source file and line (use SPDLOG_TRACE(..), SPDLOG_INFO(...) etc. instead of spdlog::trace(...)	my_file.cpp:123
%s	Basename of the source file (use SPDLOG_TRACE(..), SPDLOG_INFO(...) etc.)	my_file.cpp
%g	Full or relative path of the source file as appears in the __FILE__ macro (use SPDLOG_TRACE(..), SPDLOG_INFO(...) etc.)	/some/dir/my_file.cpp
%#	Source line (use SPDLOG_TRACE(..), SPDLOG_INFO(...) etc.)	123
%!	Source function (use SPDLOG_TRACE(..), SPDLOG_INFO(...) etc. see tweakme for pretty-print)	my_func
%o	Elapsed time in milliseconds since previous message	456
%i	Elapsed time in microseconds since previous message	456
%u	Elapsed time in nanoseconds since previous message	11456
%O	Elapsed time in seconds since previous message	4

設置輸出格式

file_logger->set_pattern("[%Y-%m-%d %H:%M:%S.%e][thread %t][%@,%!][%l] : %v");

關閉日志

//Release and close all loggers 
//把所有的log對象智能指針放置到unordered_map中去，然后調用clear函數
spdlog::drop_all();

源碼閱讀

https://www.cnblogs.com/eskylin/archive/2017/03/01/6483199.html

參考文獻

[1] https://www.cnblogs.com/oucsheep/p/8426548.html

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