Keywords: UE4 UE_LOG & ScreenDebugMessage Notes

UE_LOG

方式1：GLog
GLog->Log("Does something");
方式2：UE_LOG(LogTemp)
UE_LOG(LogTemp, Log, TEXT("%d"), 1111);
UE_LOG(LogTemp, Warning, TEXT("%d"), 1111);
方式3：一处定义，多处使用

单个头文件中声明：MyTest.h

#pragma once

MYGAME_API DECLARE_LOG_CATEGORY_EXTERN(MyTestLog, Log, All);

对应的CPP中定义：MyTest.cpp

#include "MyTest.h"

DEFINE_LOG_CATEGORY(MyTestLog);

其他cpp文件中使用：

#include "MyTest.h"

MyBlueprintLibrary::DoWork()
{
    UE_LOG(MyTestLog, Display, TEXT("Work start!"));
}

使用DECLARE_LOG_CATEGORY_EXTERN声明时，一定要加上前缀，比如 MYGAME_API。

方式4：仅在指定的单个CPP中使用

单个CPP中定义后，只在当前CPP范围内使用：

DEFINE_LOG_CATEGORY_STATIC(LogNetwork, Log, All);

其中：LogNetwork为Log名，Log为运行时log级别，All为编译期间的log级别。

方式1和方式2的输出结果
Does something
LogTemp: 1111
LogTemp: Warning: 1111（黄色）
修改log输出文件的文件名

启动命令行追加：

LOG=my_custom_log_file.log

或者：

ABSLOG=E:/my_custom_log_file.log

Low Level Log

LowLevelOutputDebugString
FPlatformMisc::LowLevelOutputDebugString(TEXT("Waited for 10 seconds on IO...."));

AddOnScreenDebugMessage

How to display screen debug message in fixed row
//display messag in second row (key = 1) when there're mulitple message in screen.
GEngine->AddOnScreenDebugMessage(1, 1.f, FColor::Green, FString("aaaaa"), false);

bNewerOnTop only works with Key == INDEX_NONE

Building Log

Build log from engine source building
D:\UnrealEngine-4.10.0-release\Engine\Programs\AutomationTool\Saved\Logs\
Build log from installed distributions of engine

TODO

Game log directory on shipping

Windows

Game: %localappdata%\<ProjectName>\Saved\Logs Server: WindowsServer\<ProjectName>\Saved\Logs (e.g Windows)

Linux

UE4 shipping log directory:
/root/.config/Epic/[YourGame]/Saved/Logs

UE4 shipping config directory:
/root/.config/Epic/[YourGame]/Saved/Config

Error Message Box

FTextBuilder ErrorMessage;
ErrorMessage.AppendLine(FText::FromString(TEXT("GPU Driver Issue.\n")));
ErrorMessage.AppendLine(FText::FromString(TEXT("Please update the latest driver.\r")));
FPlatformMisc::MessageBoxExt(EAppMsgType::Ok, *ErrorMessage.ToText().ToString(), TEXT("Error"));

FPlatformMisc::RequestExit(true, TEXT("GPU Device Issue"));

Issues

Crash in LogMacros.cpp
LogAresMessageBus: ON ACTOR SPAWNED!
LogWindows: Error: === Critical error: ===
LogWindows: Error:
LogWindows: Error: Fatal error!
LogWindows: Error:
LogWindows: Error: Unhandled Exception: EXCEPTION_ACCESS_VIOLATION reading address 0x00000001
LogWindows: Error:
LogWindows: Error: [Callstack] 0x00007ffc07e92ebd ucrtbase.dll!UnknownFunction ]
LogWindows: Error: [Callstack] 0x00007ffc07e7f10c ucrtbase.dll!UnknownFunction ]
LogWindows: Error: [Callstack] 0x00007ffc07e7eac7 ucrtbase.dll!UnknownFunction ]
LogWindows: Error: [Callstack] 0x00007ffba85398a7 UE4Editor-Core.dll!FMsg::Logf_InternalImpl() [d:\build\++ue4\sync\engine\source\runtime\core\private\logging\logmacros.cpp:99]
LogWindows: Error: [Callstack] 0x00007ffb918d55bf UE4Editor-Ares.dll!UAresMessageBus::Publish() [A:\Projekte\Unreal-Engine-4-Projekte\Ares\Source\Ares\Core\AresMessageBus.cpp:61]
LogWindows: Error: [Callstack] 0x00007ffb918d6b84 UE4Editor-Ares.dll!UAresMessageBus::execPublish() [A:\Projekte\Unreal-Engine-4-Projekte\Ares\Source\Ares\Core\AresMessageBus.h:26]

Solution:
Don’t use UE_LOG in non-GameThread of Unreal.

Crash when printing inside function
https://forums.unrealengine.com/t/crash-when-printing-inside-function/128904

Verbosity Levels

Verbosity Levels in source

Engine\Source\Runtime\Core\Public\Logging\LogVerbosity.h

/** 
 * Enum that defines the verbosity levels of the logging system.
 * Also defines some non-verbosity levels that are hacks that allow
 * breaking on a given log line or setting the color.
**/
namespace ELogVerbosity
{
    enum Type : uint8
    {
        /** Not used */
        NoLogging        = 0,

        /** Always prints a 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
    };
}
Where to change verbosity level of engine

Engine\Source\Runtime\Engine\Public\EngineLogs.h

References

Blogs

UE4日志级别设置
https://www.jianshu.com/p/c550c3223a95

[UE4] About UE_LOG
https://historia.co.jp/archives/5532/