如何使用UE_LOG(转)

在学习UE4的时候发现,想要在C++代码中输出一个log不知道要怎么办,搜了一下,发现有一个UE_LOG()的相关宏,不过好像用法很复杂.在网上找到了下边的说明,不过我代码可以直接使用C语言的printf()函数来输出log.

 
上边的代码,我的printf("aaa");没有报错,可见UE4对C语言和C++所有的东西都是原生支持的.

先上官网的使用说明:

https://wiki.unrealengine.com/Logs,_Printing_Messages_To_Yourself_During_Runtime

下边是转来的UE_LOG()用法的使用说明:

转自: http://code.roastew.com/?p=451

在Unreal Engine 4中，打Log很方便，可以使用宏：

1 2	UE_LOG ( LogTemp , Warning , TEXT ( "Your message" ) ) ;

但是使用之前需要先定义Log Category，Category会在Log中体现出来，以便在茫茫Log中更容易区分其作用或所属模块。
如果想定义只在一个CPP文件中使用的Category，不希望被其他类使用，可以定义一个Static的Category：

1 2	DEFINE_LOG_CATEGORY_STATIC ( CategoryName , Log , All ) ;

如果想定义一个‘Public’的Category，并且在全局生效，不管是static函数还是其他类都可以使用，就需要在头文件中声明一个Category，并在CPP中定义，每个用到的CPP文件都需要include该头文件:

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// in A.h DECLARE_LOG_CATEGORY_EXTERN ( CategoryName , Log , All ) // 声明一个Category为extern，避免多个文件使用此头文件时重复声明   // in A.cpp #include "A.h" DEFINE_LOG_CATEGORY ( CategoryName ) // 定义该Category，全局仅需一份   // in B.cpp #include "A.h" // 由于之前声明为extern，使用者引入头文件即可使用在A.cpp中的定义

如果想给某个定义一个专属的Category，可以使用：

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// in A.h class A { DECLARE_LOG_CATEGORY_CLASS ( CategoryName , Log , All ) ; } ;   // in A.cpp DEFINE_LOG_CATEGORY_CLASS ( A , CategoryName ) ;

定义好Log Category之后就可以使用 de style="border: 0px; font-family: Monaco, Consolas, 'Andale Mono', 'DejaVu Sans Mono', monospace; font-size: 13px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline; line-height: normal;" >UE_LOG de>了，除了最前面例子中的用法， de style="border: 0px; font-family: Monaco, Consolas, 'Andale Mono', 'DejaVu Sans Mono', monospace; font-size: 13px; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline; line-height: normal;" >UE_LOG de>的用法和C中的printf类似，支持字符串Format，例如：

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UE_LOG ( CategoryName , Warning , TEXT ( "MyCharacter's Health is %d" ) , MyCharacter - & gt ; Health ) ; UE_LOG ( CategoryName , Warning , TEXT ( "MyCharacter's Health is %f" ) , MyCharacter - & gt ; Health ) ; UE_LOG ( CategoryName , Warning , TEXT ( "MyCharacter's Name is %s" ) , * MyCharacter - & gt ; GetName ( ) ) ;

‘UE_LOG’和声明或定义Log Category的宏中提到的’Log’，’Warning’，’All’等，是ELogVerbosity中定义的枚举，具体含义可参考下面的源码。

相关源码：

声明和定义Log Category的宏：

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/** * A macro to declare a logging category as a C++ "extern" * @param CategoryName, category to declare * @param DefaultVerbosity, default run time verbosity * @param CompileTimeVerbosity, maximum verbosity to compile into the code **/ #define DECLARE_LOG_CATEGORY_EXTERN(CategoryName, DefaultVerbosity, CompileTimeVerbosity) extern struct FLogCategory ##CategoryName : public FLogCategory<ELogVerbosity::DefaultVerbosity, ELogVerbosity::CompileTimeVerbosity> { FORCEINLINE FLogCategory ##CategoryName() : FLogCategory(TEXT(#CategoryName)) {} } CategoryName ;   /** * A macro to define a logging category, usually paired with DECLARE_LOG_CATEGORY_EXTERN from the header. * @param CategoryName, category to define **/ #define DEFINE_LOG_CATEGORY(CategoryName) FLogCategory##CategoryName CategoryName;   /** * A macro to define a logging category as a C++ "static" * @param CategoryName, category to declare * @param DefaultVerbosity, default run time verbosity * @param CompileTimeVerbosity, maximum verbosity to compile into the code **/ #define DEFINE_LOG_CATEGORY_STATIC(CategoryName, DefaultVerbosity, CompileTimeVerbosity) static struct FLogCategory ##CategoryName : public FLogCategory<ELogVerbosity::DefaultVerbosity, ELogVerbosity::CompileTimeVerbosity> { FORCEINLINE FLogCategory ##CategoryName() : FLogCategory(TEXT(#CategoryName)) {} } CategoryName ;   /** * A macro to declare a logging category as a C++ "class static" * @param CategoryName, category to declare * @param DefaultVerbosity, default run time verbosity * @param CompileTimeVerbosity, maximum verbosity to compile into the code **/ #define DECLARE_LOG_CATEGORY_CLASS(CategoryName, DefaultVerbosity, CompileTimeVerbosity) DEFINE_LOG_CATEGORY_STATIC ( CategoryName , DefaultVerbosity , CompileTimeVerbosity )   /** * A macro to define a logging category, usually paired with DECLARE_LOG_CATEGORY_CLASS from the header. * @param CategoryName, category to definee **/ #define DEFINE_LOG_CATEGORY_CLASS(Class, CategoryName) Class::FLogCategory##CategoryName Class::CategoryName;

ELogVerbosity中的枚举：

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namespace ELogVerbosity { enum Type { /** Not used */ NoLogging = 0 ,   /** Always prints s fatal error to console (and log file) and crashes (even if logging is disabled) */ Fatal ,   /** * Prints an error to console (and log file). * Commandlets and the editor collect and report errors. Error messages result in commandlet failure. */ Error ,   /** * Prints a warning to console (and log file). * Commandlets and the editor collect and report warnings. Warnings can be treated as an error. */ Warning ,   /** Prints a message to console (and log file) */ Display ,   /** Prints a message to a log file (does not print to console) */ Log ,   /** * Prints a verbose message to a log file (if Verbose logging is enabled for the given category, * usually used for detailed logging) */ Verbose ,   /** * Prints a verbose message to a log file (if VeryVerbose logging is enabled, * usually used for detailed logging that would otherwise spam output) */ VeryVerbose ,   // Log masks and special Enum values   All = VeryVerbose , NumVerbosity , VerbosityMask = 0xf , SetColor = 0x40 , // not actually a verbosity, used to set the color of an output device BreakOnLog = 0x80 } ; }