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This article introduces the relevant knowledge of "how to use default in C++". In the operation of actual cases, many people will encounter such a dilemma. Then let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

ES.79: using default to handle generic case

Reason (reason)

Code clarity. Improved opportunities for error detection.

Code clarity. Increase the chances of finding errors.

Example (sample)

Enum E {a, b, c, d}

Void F1 (E x)

{

Switch (x) {

Case a:

Do_something ()

Break

Case b:

Do_something_else ()

Break

Default:

Take_the_default_action ()

Break

}

}

Here it is clear that there is a default action and that cases an and b are special.

You can clearly see that there is a default case, and an and b are special case.

Example (sample)

If there is no default action, what should you do when you only want to deal with a special case? In this case, leave an empty default processing, otherwise it is impossible to know whether you intend to handle all case or not.

Void f2 (E x)

{

Switch (x) {

Case a:

Do_something ()

Break

Case b:

Do_something_else ()

Break

Default:

/ / do nothing for the rest of the cases

Break

}

}

If default is left out, the maintainer or compiler may reasonably assume that you intend to handle all case.

Void f2 (E x)

{

Switch (x) {

Case a:

Do_something ()

Break

Case b:

Case c:

Do_something_else ()

Break

}

}

Did you forget case d or did you leave it out on purpose? Forgetting a case usually occurs when you increase the enumeration value without adding processing for that value to all switch statements.

Enforcement (implementation recommendations)

Tags switch statements of enumerated types that do not handle all enumerated values and do not contain default processing. This may produce too many false positives for some code; if this happens, the tag only handles most of the case, but not all of the case (this is the strategy adopted by very early C++ compilers).

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