.NET Framework 官方下载地址

.net framwork 官方下载地址

3.5

https://www.microsoft.com/zh-cn/download/details.aspx?id=25150

.NET Framework 4

https://www.microsoft.com/zh-cn/download/details.aspx?id=17718

.NET Framework 4.5

https://www.microsoft.com/zh-cn/download/details.aspx?id=30653

2.0

20M

https://www.microsoft.com/zh-cn/download/details.aspx?id=16614

C:\Windows\Microsoft.NET\Framework

C:\Windows\Microsoft.NET\Framework64

怎么查看4.5是否安装了

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full

如果没有Full节点，那么说明没有安装过4.5或者更新的版本

Web.config

  <system.codedom>
    <compilers>
      <compiler language="c#;cs;csharp" extension=".cs"
        type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"
        warningLevel="4" compilerOptions="/langversion:6 /nowarn:1659;1699;1701"/>
      <compiler language="vb;vbs;visualbasic;vbscript" extension=".vb"
        type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.VBCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"
        warningLevel="4" compilerOptions="/langversion:14 /nowarn:41008 /define:_MYTYPE=\&quot;Web\&quot; /optionInfer+"/>
    </compilers>
  </system.codedom>