Nesting of C language annotations

Mainstream C/C++/Java/C# Other languages , The annotation syntax is designed not to be nested .
Such as : /* xxx /* yyy */ zzz */ It's illegal. .
reason ：
Notes are used to write descriptive language , Nesting makes readability worse .

But in fact , Annotations are not just used to write annotations , It is also commonly used to mask code blocks . When you need to comment out a large program , Still use this annotation （ /* … * /） How about ？
The answer, of course, is ： Not good. ！！！
If the program to be annotated has already been annotated with this annotator , Then another annotation like this may cause problems . Some compilers are detecting "/*" Will look for the nearest " */" Combined with it .

So how to annotate large programs ？
C In language

  #if 0
  #endif

Such a statement can accomplish this task .

This is a precompiled statement , The compiler automatically recognizes the precompiled code , Judge if Is it true , If set up , Just put ****1 Code retention ,****2 Comment out the code , This is done by the compiler . This will not affect the compilation and migration of the program , Such as ：

#if 0
、
****1
/*..........*/
、
#else
、
****2
/*..........*/
、
#endif

Source of problem ：
《C Traps and defects 》

practice 1-1.
some C The compiler allows nested comments . Please write a test program , requirement ： Whether for compilers that allow nested annotations , Sea lions do not allow nested annotation compilers , The program can be compiled normally （ No error message appears ）, But the results of program execution in these two cases are different .

Tips ： In a string enclosed in double quotation marks , annotator /* Part of a string , The double quotation marks in the comments are part of the comments

Thoughts

1. To form nested annotations , This string sequence must contain ：/* /**/*/.
2. First, let's discuss ：/*/**/ . For compilers that do not allow nested annotations , This is a complete comment ; For compilers that allow nested annotations , The following characters are part of the comment .
3. Let's add ："* /", Turn it into ：/* /**/"*/".
4. For compilers that do not allow nested annotations ： The above string is equivalent to the string ："*/". Compilers that allow nested comments cannot be compiled at this time （ There is a double quotation mark left ）
5. So we followed it with a comment and a double quotation mark ：/* /**/"* /"/*" .
6. For compilers that allow nested annotations ： The above string is equivalent to "/* " ; For compilers that do not allow nested annotations ： The above string is equivalent to " * /" / *"（ Comment terminator caused by parentheses , Followed by an open comment
7. Finally, simply let the last comment end ：/* /** /"* /"/*"/**/
8. So if nested comments are allowed , The above string is equivalent to "/*" , If nested annotations are not allowed, they are equivalent to " */"

Reference link ：https://blog.csdn.net/weixin_33859693/article/details/117036478