说明：本文为Wiki上的RAMA大神文章的大致翻译

游戏模式：

在游戏模式下，你需要在游戏的快捷方式后面加 -Log，才会在游戏中显示。

 

编辑器模式（Play In Editor）：

你可以在Output窗口中看到log信息。

如果想在游戏中看到，需要到Engin.ini中修改参数添加"GameCommandLine=-log，如果没有，则需要按~，输入-Log命令开启。

 

快速使用：

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

不用设置标签，简单快速。

 

设置拥有自己标签的Log：

在你的游戏头文件中加入：

//General LogDECLARE_LOG_CATEGORY_EXTERN(YourLog, Log, All); //Logging during game startupDECLARE_LOG_CATEGORY_EXTERN(YourInit, Log, All); //Logging for your AI systemDECLARE_LOG_CATEGORY_EXTERN(YourAI, Log, All); //Logging for Critical Errors that must always be addressedDECLARE_LOG_CATEGORY_EXTERN(YourCriticalErrors, Log, All);

这样输出的Log你就可以知道是哪个部分的，这也是UE_Log很有用的原因。

在你的游戏Cpp文件中：

//General LogDEFINE_LOG_CATEGORY(YourLog); //Logging during game startupDEFINE_LOG_CATEGORY(YourInit); //Logging for your AI systemDEFINE_LOG_CATEGORY(YourAI); //Logging for Critical Errors that must always be addressedDEFINE_LOG_CATEGORY(YourCriticalErrors);

Log格式：

Log Message

//"This is a message to yourself during runtime!"UE_LOG(YourLog,Warning,TEXT("This is a message to yourself during runtime!"));

Log an FString

%s strings are wanted as TCHAR* by Log, so use *FString()//"MyCharacter's Name is %s"UE_LOG(YourLog,Warning,TEXT("MyCharacter's Name is %s"), *MyCharacter->GetName() );

Log an Int

//"MyCharacter's Health is %d"UE_LOG(YourLog,Warning,TEXT("MyCharacter's Health is %d"), MyCharacter->Health );

Log a Float

//"MyCharacter's Health is %f"UE_LOG(YourLog,Warning,TEXT("MyCharacter's Health is %f"), MyCharacter->Health );

Log an FVector

//"MyCharacter's Location is %s"UE_LOG(YourLog,Warning,TEXT("MyCharacter's Location is %s"),     *MyCharacter->GetActorLocation().ToString());

Log an FName

//"MyCharacter's FName is %s"UE_LOG(YourLog,Warning,TEXT("MyCharacter's FName is %s"),     *MyCharacter->GetFName().ToString());

Log an FString,Int,Float

//"%s has health %d, which is %f percent of total health"UE_LOG(YourLog,Warning,TEXT("%s has health %d, which is %f percent of total health"),    *MyCharacter->GetName(), MyCharacter->Health, MyCharacter->HealthPercent);

Log的颜色设置：

//"this is Grey Text"UE_LOG(YourLog,Log,TEXT("This is grey text!"));//"this is Yellow Text"UE_LOG(YourLog,Warning,TEXT("This is yellow text!"));//"This is Red Text"UE_LOG(YourLog,Error,TEXT("This is red text!"));

可以看得出第二个参数是是用来控制颜色的。

 

传递客户端信息（网络模式）：

PlayerController->ClientMessage("Your Message");

命令行命令以及Engine.ini配置：

Log conventions (in the console, ini files, or environment variables)

[cat] = a category for the command to operate on, or 'global' for all categories.标签，没有设置就显示所有的Log[level] = verbosity level, one of: none, error, warning, display, log, verbose, all, default关卡，显示某某关卡的Log

At boot time, compiled in default is overridden by ini files setting, which is overridden by command line

Log console command usage

Log list - list all log categoriesLog list [string] - list all log categories containing a substringLog reset - reset all log categories to their boot-time defaultLog [cat] - toggle the display of the category [cat]Log [cat] off - disable display of the category [cat]Log [cat] on - resume display of the category [cat]Log [cat] [level] - set the verbosity level of the category [cat]Log [cat] break - toggle the debug break on display of the category [cat]

Log command line

-LogCmds=\"[arguments],[arguments]...\"           - applies a list of console commands at boot time-LogCmds=\"foo verbose, bar off\"         - turns on the foo category and turns off the bar category

Environment variables

Any command line option can be set via the environment variable UE-CmdLineArgs

set UE-CmdLineArgs=\"-LogCmds=foo verbose breakon, bar off\"

Config file

In DefaultEngine.ini or Engine.ini:

[Core.Log]global=[default verbosity for things not listed later][cat]=[level]foo=verbose break

Rama后面的一篇文章提供了显示代码行号、函数名称、类名等功能：https://wiki.unrealengine.com/Logs,_Printing_the_Class_Name,_Function_Name,_Line_Number_of_your_Calling_Code!