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 Log DECLARE_LOG_CATEGORY_EXTERN(YourLog, Log, All); //Logging during game startup DECLARE_LOG_CATEGORY_EXTERN(YourInit, Log, All); //Logging for your AI system DECLARE_LOG_CATEGORY_EXTERN(YourAI, Log, All); //Logging for Critical Errors that must always be addressed DECLARE_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 Log DEFINE_LOG_CATEGORY(YourLog); //Logging during game startup DEFINE_LOG_CATEGORY(YourInit); //Logging for your AI system DEFINE_LOG_CATEGORY(YourAI); //Logging for Critical Errors that must always be addressed DEFINE_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 categories Log list [string] - list all log categories containing a substring Log reset - reset all log categories to their boot-time default Log [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!