UE4之宏与预编译指令定义

在UBT中添加宏定义

UnrealEngine\Engine\Source\Programs\UnrealBuildTool\Configuration\ModuleRules.cs

UnrealEngine\Engine\Source\Programs\UnrealBuildTool\Configuration\UEBuildPlatform.cs

UnrealEngine\Engine\Source\Programs\UnrealBuildTool\Configuration\UEBuildTarget.cs

UnrealEngine\Engine\Source\Programs\UnrealBuildTool\Platform\Android\UEBuildAndroid.cs

UnrealEngine\Engine\Source\Programs\UnrealBuildTool\Platform\IOS\UEBuildIOS.cs

UnrealEngine\Engine\Source\Runtime\Core\Core.Build.cs

Definitions文件

Definitions文件是编译时存放所有定义的宏

编译编辑器(Debug)时，这些宏会被写入Intermediate\Build\Win64\UE4Editor\Debug\<Module>\Definitions.<Module>.h中

编译win64的cook版本(Debug)时，这些宏会被写入Intermediate\Build\Win64\<MyGame>\Debug\<Module>\Definitions.<Module>.h中

编译Android的cook版本(Debug)时，这些宏会被写入Intermediate\Build\Android\<MyGame>\Debug\<Module>\Definitions.<Module>.h中

编译IOS的cook版本(Debug)时，这些宏会被写入Intermediate\Build\IOS\<MyGame>\Debug\<Module>\Definitions.<Module>.h中

ue4.26在vs2019缺省用c++14编译

注：Intermediate\ProjectFiles\*vcxproj工程文件的生成代码在G:\svn\UnrealEngine\Engine\Source\Programs\UnrealBuildTool\ProjectFiles\VisualStudio\VCProject.cs

使用__cplusplus宏在代码中判断c++标准库版本：

if (__cplusplus == 201703L)
{
    UE_LOG(LogTemp, Log, TEXT("C++17."));
}
else if (__cplusplus == 201402L)
{
    UE_LOG(LogTemp, Log, TEXT("C++14."));
}
else if (__cplusplus == 201103L)
{
    UE_LOG(LogTemp, Log, TEXT("C++11."));
}    
else if (__cplusplus == 199711L)
{
    UE_LOG(LogTemp, Log, TEXT("C++98."));
}
else
{
    UE_LOG(LogTemp, Log, TEXT("pre-standard C++."));
}

基础宏

UnrealEngine\Engine\Source\Runtime\Core\Public\HAL\PreprocessorHelpers.h

UnrealEngine\Engine\Source\Runtime\Core\Public\Misc\Build.h

UnrealEngine\Engine\Source\Runtime\Core\Public\HAL\Platform.h

预编译相关的宏

不同平台下，该宏的实现详见如下文件

UnrealEngine\Engine\Source\Runtime\Core\Public\Android\AndroidPlatformCompilerPreSetup.h
UnrealEngine\Engine\Source\Runtime\Core\Public\Apple\ApplePlatformCompilerPreSetup.h
UnrealEngine\Engine\Source\Runtime\Core\Public\Clang\ClangPlatformCompilerPreSetup.h
UnrealEngine\Engine\Source\Runtime\Core\Public\GenericPlatform\GenericPlatformCompilerPreSetup.h
UnrealEngine\Engine\Source\Runtime\Core\Public\HoloLens\HoloLensPlatformCompilerPreSetup.h
UnrealEngine\Engine\Source\Runtime\Core\Public\IOS\IOSPlatformCompilerPreSetup.h
UnrealEngine\Engine\Source\Runtime\Core\Public\Linux\LinuxPlatformCompilerPreSetup.h
UnrealEngine\Engine\Source\Runtime\Core\Public\Lumin\LuminPlatformCompilerPreSetup.h
UnrealEngine\Engine\Source\Runtime\Core\Public\Mac\MacPlatformCompilerPreSetup.h
UnrealEngine\Engine\Source\Runtime\Core\Public\Unix\UnixPlatformCompilerPreSetup.h
UnrealEngine\Engine\Source\Runtime\Core\Public\Windows\WindowsPlatformCompilerPreSetup.h

编译用命令行文件

TargetCode.response内容如下：

/D_CRT_STDIO_LEGACY_WIDE_SPECIFIERS=1
/D_SILENCE_STDEXT_HASH_DEPRECATION_WARNINGS=1
/D_WINDLL
/D_DISABLE_EXTENDED_ALIGNED_STORAGE

。。。 。。。

/DUE_BUILD_DEBUG=1
/DWITH_EDITOR=1
/DWITH_ENGINE=1
/DWITH_UNREAL_DEVELOPER_TOOLS=0
/DWITH_PLUGIN_SUPPORT=0
/DUE_BUILD_MINIMAL=0
/DIS_MONOLITHIC=0
/DIS_PROGRAM=0
/DPLATFORM_WINDOWS=1
/DOVERRIDE_PLATFORM_HEADER_NAME=Windows

/source-charset:utf-8
/execution-charset:utf-8
/I .
/I D:\svn\ThirdParty

/I ... ... 
/I D:\svn\TPSProject\Private

/EP
"D:\svn\TPSProject\Private\TargetCode.cpp"

x64 Native Tools Command Prompt for VS2019

cd /d %EngineDir%\Engine\Source

cl.exe @"G:\TargetCode.response" > "G:\TargetCode.i.cpp"

#include头文件

包括外部模块的头文件时，只用写Public、Classes文件夹之后的相对目录。

包含内部模块的头文件时，除了写Public、Classes文件夹之后的相对目录，还可以只用写Private文件夹之后的相对目录。

具体逻辑详见：UnrealEngine\Engine\Source\Programs\UnrealBuildTool\Configuration\UEBuildModuleCPP.cs的AddDefaultIncludePaths函数

private void AddDefaultIncludePaths()
{
    // Add the module's parent directory to the public include paths, so other modules may include headers from it explicitly.
    foreach (DirectoryReference ModuleDir in ModuleDirectories)
    {
        PublicIncludePaths.Add(ModuleDir.ParentDirectory);

        // Add the base directory to the legacy include paths.
        LegacyPublicIncludePaths.Add(ModuleDir);

        // Add the 'classes' directory, if it exists
        DirectoryReference ClassesDirectory = DirectoryReference.Combine(ModuleDir, "Classes");
        if (DirectoryLookupCache.DirectoryExists(ClassesDirectory))
        {
            PublicIncludePaths.Add(ClassesDirectory);
        }

        // Add all the public directories
        DirectoryReference PublicDirectory = DirectoryReference.Combine(ModuleDir, "Public");
        if (DirectoryLookupCache.DirectoryExists(PublicDirectory))
        {
            PublicIncludePaths.Add(PublicDirectory);

            ReadOnlyHashSet<string> ExcludeNames = UEBuildPlatform.GetBuildPlatform(Rules.Target.Platform).GetExcludedFolderNames();
            EnumerateLegacyIncludePaths(DirectoryItem.GetItemByDirectoryReference(PublicDirectory), ExcludeNames, LegacyPublicIncludePaths);
        }

        // Add the base private directory for this module
        DirectoryReference PrivateDirectory = DirectoryReference.Combine(ModuleDir, "Private");
        if (DirectoryLookupCache.DirectoryExists(PrivateDirectory))
        {
            PrivateIncludePaths.Add(PrivateDirectory);
        }
    }
}

如：UnrealEngine\Engine\Source\Runtime\Engine\Public\SceneManagement.h  写成

#include "SceneManagement.h"

如：UnrealEngine\Engine\Source\Runtime\Engine\Classes\GameFramework\Actor.h  写成

#include "GameFramework/Actor.h"

如果只想用GEngine，只需要#include "Engine/Engine.h"就行，不要用#include "Engine.h"（#include "Engine.h"里面加了一大堆其他头文件，非常容易与windows sdk发生冲突，导致一些奇怪的编译错误）

UnrealEngine\Engine\Source\Runtime\Engine\Classes\Engine\Engine.h  // #include "Engine.h"

UnrealEngine\Engine\Source\Runtime\Engine\Public\Engine.h  // #include "Engine/Engine.h"

跨平台目录说明

注1：Lumin是Magic Leap公司基于Linux和Android开发的穿戴式设备操作系统，目前已用在自家产品Magic Leap One AR头盔中

注2：HoloLens是Microsoft公司基于win10开发的混合现实的穿戴式设备操作系统，目前已用在自家产品HoloLens AR头盔中

注3：GenericPlatform提供公共基类，Windows、Linux、Unix、Mac、Apple、HoloLens、Lumin、Android、IOS从GenericPlatform上派生来实现各平台的功能

注4：通过HAL来对外提供统一的接口。其他模块仅需要include HAL目录下的头文件即可