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This article introduces the knowledge of "why C++ clearly defines a single-parameter constructor by default". Many people will encounter such a dilemma in the operation of actual cases. 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!

C.46: a single parameter constructor Reason is clearly defined by default (reason)

Avoid unexpected conversions.

Example, bad (negative example)

Class String {

Public:

String (int); / / BAD

/ /...

}

String s = 10; / / surprise: string of size 10Exception (exception)

If you do need an implicit type conversion from constructor arguments like class types, do not use the explicit keyword.

Class Complex {

Public:

Complex (double d); / / OK: we want a conversion from d to {d, 0}

/ /...

}

Complex z = 10.7; / / unsurprising conversion Exception (exception)

Copy and move constructors should not be defined as explicit, because type conversions will not be performed. Explicit copy / move constructors make it difficult to pass parameters and return results by value.

Enforcement (implementation recommendations)

(simple) the constructor with unique parameters should be defined as explicit. Well-defined non-explicit single-argument constructors are rare in most code. Give a warning for all situations that are not in the positive list.

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