引擎版本获取

有些需求工程中需要检测引擎版本，如在支持多个引擎版本的插件，在引擎中包含不同的模块，引擎版本之间 API 的差异等。

C++ 获取引擎版本

Runtime/Launch/Resources/Version.h 中有版本宏定义：

Runtime/Launch/Resources/Version.h

// newer than a 4.11.* version, regardless of the changelist that it was built with)
#define ENGINE_MAJOR_VERSION	4
#define ENGINE_MINOR_VERSION	26
#define ENGINE_PATCH_VERSION	2

在代码中通过预处理指令即可使用。

从 TargetRules 获取引擎版本

TargetRules 中具有 Version(ReadOnlyBuildVersion)成员，它是 BuildVersion 的类型，定义在 Programs\UnrealBuildTool\System\BuildVersion.cs 中。

// UnrealBuildTools/System/BuildVersion.cs
namespace UnrealBuildTool
{
	/// <summary>
	/// Holds information about the current engine version
	/// </summary>
	[Serializable]
	public class BuildVersion
	{
		/// <summary>
		/// The major engine version (4 for UE4)
		/// </summary>
		public int MajorVersion;

		/// <summary>
		/// The minor engine version
		/// </summary>
		public int MinorVersion;

		/// <summary>
		/// The hotfix/patch version
		/// </summary>
		public int PatchVersion;

		/// <summary>
		/// The changelist that the engine is being built from
		/// </summary>
		public int Changelist;

		/// <summary>
		/// The changelist that the engine maintains compatibility with
		/// </summary>
		public int CompatibleChangelist;

		/// <summary>
		/// Whether the changelist numbers are a licensee changelist
		/// </summary>
		public bool IsLicenseeVersion;

		/// <summary>
		/// Whether the current build is a promoted build, that is, built strictly from a clean sync of the given changelist
		/// </summary>
		public bool IsPromotedBuild;

		/// <summary>
		/// Name of the current branch, with '/' characters escaped as '+'
		/// </summary>
		public string BranchName;

		/// <summary>
		/// The current build id. This will be generated automatically whenever engine binaries change if not set in the default Engine/Build/Build.version.
		/// </summary>
		public string BuildId;

		/// <summary>
		/// The build version string
		/// </summary>
		public string BuildVersionString;
        
        // ...
   	}
}

其中的 MajorVersion/MinorVersion/PatchVersion 分别对应 X.XX.X。

在 UE4.19 版本之前从 UBT 获取引擎版本比较麻烦：

BuildVersion Version;
if (BuildVersion.TryRead(BuildVersion.GetDefaultFileName(), out Version))
{
    System.Console.WriteLine(Version.MajorVersion);
    System.Console.WriteLine(Version.MinorVersion);
    System.Console.WriteLine(Version.PatchVersion);
}

在 UE4.19 及以后的引擎版本，可以通过 ReadOnlyTargetRules.Version 来获得，它是 ReadOnlyBuildVersion 类型，包裹了一个 BuildVersion 类。

可以在 Target.cs 或者 Build.cs 里通过 Target.Version 来访问引擎版本，可以根据不同的引擎版本来使用不同的库。