Use of explicit keywords in C + +

Read a book see explicit key words, to make a note, speak more clear, relatively shallow.

In C + +, we can sometimes use constructors as automatic type conversion functions. However, this automatic feature is not always desirable and sometimes results in unexpected type conversions, so C + + has a new keyword explicit to turn off this automatic feature. That is, the class constructor that is decorated with the explicit keyword, cannot be automatically implicitly type-converted, and can only be explicitly type-cast.

Note: The constructor for only one parameter, or the constructor has n parameters, but there are n-1 parameters that provide the default value for the type conversion.

Here's a code to illustrate the application (no explicit scenario):

1 /*Example code 1*/2 classDemo3 {4     Public:5 Demo (); / * Constructor 1 *    /6Demo (Doublea); / * Sample code 2 *    /7Demo (intADoubleb); / * Sample Code 3 *    /8Demo (intAintb=Ten,DoubleC=1.6); / * Sample code 4 *    /9~Demo ();Ten     voidFunc (void); One  A     Private: -     intvalue1; -     intvalue2; the};

These four constructors:

Constructor 1 does not have parameters and cannot be converted by type!

Constructor 2 has a parameter that can be converted to type, such as: Demo test; Test = 12.2; Such a call would be equivalent to converting 12.2 implicitly to the demo type.

Constructor 3 has two parameters and no default value, so type conversion cannot be used!

Constructor 4 has 3 parameters, of which two parameters have default values, it can be implicitly converted, such as: Demo test;test = 10; 。

Here's what happens when you use the keyword explicit:

1  1 /*Example code 2*/2  2 classDemo3  3 {4  4     Public:5  5Demo ();/*Constructor 1*/6  6     ExplicitDemo (Doublea);/*Example code 2*/7  7Demo (intADoubleb);/*Example Code 3*/8  8  9  9~Demo ();Ten Ten     voidFunc (void); One  One  A  A     Private: -  -     intvalue1; -  -     intvalue2; the  the};

In the above constructor 2, implicit conversions cannot be made because the explicit keyword is used. That is: Demo test;test = 12.2; is invalid! But we can do display type conversions, such as:

Demo test;

Test = Demo (12.2); Or

Test = (Demo) 12.2;

Use of explicit keywords in C + +