Converting constructor

cppreference Converting constructor

What is converting constructor？

A constructor that is not declared with the specifier explicit and which can be called with a single parameter (until C++11) is called a converting constructor.

Implicitly-declared and user-defined non-explicit copy constructors and move constructors are converting constructors.

NOTE:

1、从C++11开始，对"single parameter"放开了限制，允许有多个parameter，后面描述了这样的example

Unlike explicit constructors, which are only considered during direct initialization (which includes explicit conversions such as static_cast), converting constructors are also considered during copy initialization, as part of user-defined conversion sequence.

NOTE:

1、这是取自下面的例子:

A a1 = 1;      // OK: copy-initialization selects A::A(int)

2、上述 user-defined conversion sequence ，其实就是 implicit conversion

3、copy constructor会参与两种initialization:

copy initialization 和 direct initialization

It is said that a converting constructor specifies an implicit conversion from the types of its arguments (if any) to the type of its class. Note that non-explicit user-defined conversion function also specifies an implicit conversion.