VS2017 - 框架4.6.2不是在c＃中的类库项目中显示的选项，但它是在一个vb窗体中的一个窗体中(VS2017 - Framework 4.6.2 is not shown as an option in a class library project in c#, but it is in a vb windows forms one)

 CMD有许多具有特殊含义的字符，通常被称为“毒性字符”，因为如果它们暴露给批处理解析器，它们可能会导致许多不需要的影响。 示例包括& | > < - 还有更多。 
 
 通常，如果字符引用为">" ，或者像^>那样转义，则不会导致问题。 但是你无法控制用户输入的内容。 使用正常扩展时，某些值不安全。 例如，如果用户输入This & that "& the other thing" ，则无法在值周围添加引号，以便引用两个& 。 
 
 值得庆幸的是，延迟扩展提供了一个简单的解 而不是使用%VAR%扩展变量，而是使用!VAR! 。 解析器完成查看所有字符后扩展变量，因此毒性字符不会导致任何问题。 必须首先使用setlocal enableDelayedExpansion启用延迟扩展 
 
 这是一个简单的演示，无论出现什么毒性字符，都可以成功地ECHO用户键入的任何值。 您可以轻松地将代码调整为IF语句。 
 
@echo off
setlocal enableDelayedExpansion
set /p "var=Enter a string: "
echo You entered: !var!

CMD has many characters that have special meaning that are often referred to as "poison characters" because they can lead to many unwanted effects if they are exposed to the batch parser. Examples include & | > < - there are more.
 
Generally, the characters do not cause problems if they are either quoted like ">", or escaped like ^>. But you don't have control over what the user enters. Some values simply are not safe to work with using normal expansion. For example, if the user enters This & that "& the other thing", then there is no way to add quotes around the value such that both & are quoted.
 
Thankfully, delayed expansion provides a simple solution. Instead of expanding a variable using %VAR%, you use !VAR!. The variable is expanded after the parser finishes looking at all the characters, so the poison characters do not cause any problem. Delayed expansion must first be enabled by using setlocal enableDelayedExpansion
 
Here is a simple demonstration that will successfully ECHO any value the user types in, no matter what poison characters are present. You can easily adapt the code to an IF statement.
 
@echo off
setlocal enableDelayedExpansion
set /p "var=Enter a string: "
echo You entered: !var!