正如前面《日志庫EasyLogging++學習系列（3）—— 配置功能》文中最后提到的，在某些應用場景下，我們還需要通過其他的一些配置手段來輔助我們完成某些特殊功能，這些輔助配置手段包括設置命令行參數、設置日志標記、配置宏定義。本文中就對這幾個輔助配置功能逐一進行簡要介紹。

命令行參數

在 Easylogging++ 中可以通過START_EASYLOGGINGPP(argc, argv)?來完成命令行參數的設置，下面的表格列舉了GitHub上給出的 Easylogging++ 支持的命令行參數：

ArgumentDescription

-v	Activates maximum verbosity
--v=2	Activates verbosity upto verbose level 2 (valid range: 0-9)
--verbose	Activates maximum verbosity
-vmodule=MODULE_NAME	Activates verbosity for files starting with main to level 1, the rest of the files depend on logging flag?AllowVerboseIfModuleNotSpecified?Please see Logging Flags section above. Two modules can be separated by comma. Please note vmodules are last in order of precedence of checking arguments for verbose logging, e.g, if we have -v in application arguments before vmodules, vmodules will be ignored.
--logging-flags=3	Sets logging flag. In example?i.e, 3, it sets logging flag toNewLineForContainer?and?AllowVerboseIfModuleNotSpecified. See logging flags section above for further details and values. See macros section to disable this function.
--default-log-file=FILE	Sets default log file for existing and future loggers. You may want to consider defining?ELPP_NO_DEFAULT_LOG_FILE?to prevent creation of default empty log file during pre-processing. See macros section to disable this function.

對于上述命令行參數，有必要簡單說明一下：

• 其中的 -v 、 --v 、 --verbose 、 -vmodule 都是用來設置 Verbose 詳細日志的，而且這幾個參數之間是有優先級順序的，如下：-v ?優先于 --verbose 優先于 --v 優先于 -vmodule。但是，在效果上 -v 和 --verbose 是一樣的。請看下面的例子：

命令行參數例一：--v=2 -v ，在這里參數 --v=2 會被參數 -v 覆蓋，因為 -v 優先級最高。

命令行參數例二：--verbose -vmodule=main=3 ，在這里參數 -vmodule=main=3?會被參數 --verbose 覆蓋，因為 --verbose?優先于 -vmodule?。

命令行參數例三：-vmodule=main*=3 --v=5 -v --verbose ，在這里參數 -v 會覆蓋其他所有的參數，因為 -v 優先級最高。

• 其中的 --logging-flags 是用來設置日志標記的，而且必須定義?ELPP_LOGGING_FLAGS_FROM_ARG?這個宏定義。

• 其中的 --default-log-file 是用來設置日志默認保存文件名的。如果沒用這個命令行參數設置文件名，那么默認的文件名就是?logs\\myeasylog.log 。另外，我們也可以用宏定義?ELPP_DEFAULT_LOG_FILE?來達到相同的效果。如：#defineELPP_DEFAULT_LOG_FILE "logs\\tem\\test.log" 。

下面的代碼演示了設置命令行參數 --v=2 ，其最終效果是 VLOG(3) 將會被屏蔽： [cpp] view plaincopy print?

#include?"easylogging++.h"??

??

INITIALIZE_EASYLOGGINGPP??

??

int?main(int?argc,?char**?argv)??

{??

????///?請自行加上命令行參數?--v=2，否則達不到演示的效果??

????START_EASYLOGGINGPP(argc,?argv);??

??

????VLOG(0);??

????VLOG(1);??

????VLOG(2);??

????VLOG(3);??

??

????system("pause");??

????return?0;??

}??

#include "easylogging++.h"INITIALIZE_EASYLOGGINGPPint main(int argc, char** argv) {/// 請自行加上命令行參數 --v=2，否則達不到演示的效果START_EASYLOGGINGPP(argc, argv);VLOG(0);VLOG(1);VLOG(2);VLOG(3);system("pause");return 0; }更多關于Verbose日志的詳細信息請參考《日志庫EasyLogging++學習系列（8）—— Verbose日志詳解》。

日志標記

在學習日志標記之前，我們先來看看 Easylogging++ 提供出來的三個和日志標記緊密相關的功能接口函數：

• 增加標記函數：?el::Loggers::addFlag?

• 刪除標記函數：el::Loggers::removeFlag?

• 檢查標記函數：el::Loggers::hasFlag?

下面的表格列舉了GitHub上給出的 Easylogging++ 支持的日志標記：

FlagDescription

NewLineForContainer (1)	Makes sure we have new line for each Container log entry
AllowVerboseIfModuleNotSpecified (2)	Makes sure if -vmodule is used and does not specifies a module, then verbose logging is allowed via that module. Say param was -vmodule=main*=3 and a verbose log is being written from a file called something.cpp then if this flag is enabled, log will be written otherwise it will be disallowed. Note: having this defeats purpose of -vmodule
LogDetailedCrashReason (4)	When handling crashes by default, detailed crash reason will be logged as well (Disabled by default) (issue #90)
DisableApplicationAbortOnFatalLog (8)	Allows to disable application abortion when logged using FATAL level. Note that this does not apply to default crash handlers as application should be aborted after crash signal is handled. (Not added by default) (issue #119)
ImmediateFlush (16)	Flushes log with every log-entry (performance sensative) - Disabled by default
StrictLogFileSizeCheck (32)	Makes sure log file size is checked with every log
ColoredTerminalOutput (64)	Terminal output will be colorful if supported by terminal.
MultiLoggerSupport (128)	Enables support for using multiple loggers to log single message. (E.g,?CLOG(INFO, "default", "network") << This will be logged using default and network loggers;)
DisablePerformanceTrackingCheckpointComparison (256)	Disables checkpoint comparison
DisableVModules (512)	Disables usage of vmodules
DisableVModulesExtensions (1024)	Disables vmodules extension. This means if you have a vmodule -vmodule=main*=4 it will cover everything starting with main, where as if you do not have this defined you will be covered for any file starting with main and ending with one of the following extensions; .h .c .cpp .cc .cxx .-inl-.h .hxx .hpp. Please note following vmodule is not correct -vmodule=main.=4 with this macro not defined because this will check for main..c, notice double dots. If you want this to be valid, have a look at logging flag above: AllowVerboseIfModuleNotSpecified '?' and '' wildcards are supported
HierarchicalLogging (2048)	Enables hierarchical logging. This is not applicable to verbose logging.
CreateLoggerAutomatically (4096)	Creates logger automatically when not available.
AutoSpacing (8192)	Automatically adds spaces. E.g,LOG(INFO) << "DODGE" << "THIS!";?will output "DODGE THIS!"
FixedTimeFormat (16384)	Applicable to performace tracking only - this prevents formatting time. E.g,?1001 ms?will be logged as is, instead of formatting it as?1.01 sec

對于上述的日志標記，可在 Easylogging++ 源碼中查看枚舉值el::LoggingFlag?，每個標記的含義在表格和源碼中都描述得比較清楚了，不過還是建議大家都親自動手試一試，下面的代碼演示了標記?NewLineForContainer?的作用：

[cpp] view plaincopy print?

#define?ELPP_STL_LOGGING??

#include?"easylogging++.h"??

??

INITIALIZE_EASYLOGGINGPP??

??

int?main(int?argc,?char**?argv)??

{??

????std::vector<int>?vecNum;??

????vecNum.push_back(1);??

????vecNum.push_back(2);??

????vecNum.push_back(3);??

??

????///?增加標記?NewLineForContainer，注意查看輸出STL容器的效果??

????el::Loggers::addFlag(el::LoggingFlag::NewLineForContainer);??

????LOG(INFO)?<<?vecNum;??

??

????///?刪除標記?NewLineForContainer，注意查看輸出STL容器的效果??

????el::Loggers::removeFlag(el::LoggingFlag::NewLineForContainer);??

????LOG(INFO)?<<?vecNum;??

??????

????system("pause");??

????return?0;??

}??

#define ELPP_STL_LOGGING #include "easylogging++.h"INITIALIZE_EASYLOGGINGPPint main(int argc, char** argv) {std::vector<int> vecNum;vecNum.push_back(1);vecNum.push_back(2);vecNum.push_back(3);/// 增加標記 NewLineForContainer，注意查看輸出STL容器的效果el::Loggers::addFlag(el::LoggingFlag::NewLineForContainer);LOG(INFO) << vecNum;/// 刪除標記 NewLineForContainer，注意查看輸出STL容器的效果el::Loggers::removeFlag(el::LoggingFlag::NewLineForContainer);LOG(INFO) << vecNum;system("pause");return 0; }

配置宏定義

在 Easylogging++ 中，有些功能必須定義相應的宏定義才能開啟。為了方便記憶，Easylogging++ 中所有的宏定義都是以 ELPP_ 開頭的，所以可以在源碼中搜索 ELPP_ 來查看都定義了哪些宏定義。下面的表格列舉了GitHub上給出的 Easylogging++ 支持的宏定義（只列舉了部分）：

Macro NameDescription

ELPP_DEBUG_ASSERT_FAILURE	Aborts application on first assertion failure. This assertion is due to invalid input e.g, invalid configuration file etc.
ELPP_UNICODE	Enables Unicode support when logging. RequiresSTART_EASYLOGGINGPP
ELPP_THREAD_SAFE	Enables thread-safety - make sure -lpthread linking for Linux.
ELPP_FORCE_USE_STD_THREAD	Forces to use C++ standard library for threading (Only useful when using?ELPP_THREAD_SAFE
ELPP_STACKTRACE_ON_CRASH	Applicable to GCC only. Enables stacktrace on application crash
ELPP_DISABLE_DEFAULT_CRASH_HANDLING	Disables default crash handling. You can use el::Helpers::setCrashHandler to use your own handler.
ELPP_DISABLE_LOGS	Disables all logs - (preprocessing)
ELPP_DISABLE_DEBUG_LOGS	Disables debug logs - (preprocessing)
ELPP_DISABLE_INFO_LOGS	Disables info logs - (preprocessing)
ELPP_DISABLE_WARNING_LOGS	Disables warning logs - (preprocessing)
ELPP_DISABLE_ERROR_LOGS	Disables error logs - (preprocessing)
ELPP_DISABLE_FATAL_LOGS	Disables fatal logs - (preprocessing)
ELPP_DISABLE_VERBOSE_LOGS	Disables verbose logs - (preprocessing)
ELPP_DISABLE_TRACE_LOGS	Disables trace logs - (preprocessing)
ELPP_FORCE_ENV_VAR_FROM_BASH	If environment variable could not be found, force using alternative bash command to find value, e.g,whoami?for username. (DO NOT USE THIS MACRO WITH?LD_PRELOAD?FOR LIBRARIES THAT ARE ALREADY USING Easylogging++ OR YOU WILL END UP IN STACK OVERFLOW FOR PROCESSES (popen) (see?issue #87?for details))
ELPP_DEFAULT_LOG_FILE	Full filename where you want initial files to be created. You need to embed value of this macro with quotes, e.g,?-DELPP_DEFAULT_LOG_FILE='"logs/el.gtest.log"'Note the double quotes inside single quotes, double quotes are the values for?const char*?and single quotes specifies value of macro
ELPP_NO_DEFAULT_LOG_FILE	If you dont want to initialize library with default log file, define this macro. But be sure to configure your logger with propery log filename or you will end up getting heaps of errors when trying to log to file (andTO_FILE?is configured to?true)
ELPP_DEBUG_ERRORS	If you wish to find out internal errors raised by Easylogging++ that can be because of configuration or something else, you can enable them by defining this macro. You will get your errors on standard output i.e, terminal or command prompt.
ELPP_DISABLE_CUSTOM_FORMAT_SPECIFIERS	Forcefully disables custom format specifiers
ELPP_DISABLE_LOGGING_FLAGS_FROM_ARG	Forcefully disables ability to set logging flags using command-line arguments
ELPP_DISABLE_LOG_FILE_FROM_ARG	Forcefully disables ability to set default log file from command-line arguments
ELPP_WINSOCK2	On windows system force to use?winsock2.hinstead of?winsock.h?when?WIN32_LEAN_AND_MEANis defined

利用在上述的宏定義，可以完成一些配置文件中無法完成的配置。下面簡單介紹幾個比較實用的宏定義：

• ELPP_DEBUG_ASSERT_FAILURE?宏定義，可以幫助我們檢測配置文件中的配置項名稱是否正確，假如配置項名稱不是Easylogging++ 支持的，那么就會出現斷言中斷。

• ELPP_UNICODE?宏定義，默認的日志記錄是只支持多字節字符串的，同時使用這個宏定義和?START_EASYLOGGINGPP(argc, argv) 可以開啟 Unicode 字符串記錄日志的功能。

• ELPP_THREAD_SAFE?宏定義，在默認情況下，考慮到性能，多線程安全功能是關閉的，使用這個宏定義則可以開啟。

• ELPP_STL_LOGGING?宏定義，使 Easylogging++ 支持STL模板和容器類型的日志輸出，比如上面第二部分介紹日志標記最后給出例子。考慮到性能，每個容器最大容量是 100，可以通過修改源碼改變這個限制，但不建議這么做，除非你可以無視性能和效率。

當然，其他的宏定義也很實用，建議大家也可以親自試一試，看看其實際的作用。需要注意的是，有些宏必須在包含?Easylogging++ 頭文件之前，即必須在代碼?#include "easylogging++.h" 之前完成定義才有意義。下面的代碼演示了宏定義 ELPP_UNICODE?的作用： [cpp] view plaincopy print?

#define?ELPP_UNICODE??

#include?"easylogging++.h"??

??

INITIALIZE_EASYLOGGINGPP??

??

int?main(int?argc,?char**?argv)??

{??

????///?同時使用?START_EASYLOGGINGPP?才能使用Unicode???

????START_EASYLOGGINGPP(argc,?argv);??

??

????LOG(INFO)?<<?L"宏定義演示。";??

??

????system("pause");??

????return?0;??

}??

#define ELPP_UNICODE #include "easylogging++.h"INITIALIZE_EASYLOGGINGPPint main(int argc, char** argv) {/// 同時使用 START_EASYLOGGINGPP 才能使用Unicode START_EASYLOGGINGPP(argc, argv);LOG(INFO) << L"宏定義演示。";system("pause");return 0; }

總結

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