2.2 KiB
[class.conv.ctor]
11 Classes [class]
11.4 Class members [class.mem]
11.4.8 Conversions [class.conv]
11.4.8.2 Conversion by constructor [class.conv.ctor]
A constructor that is not explicit ([dcl.fct.spec]) specifies a conversion from the types of its parameters (if any) to the type of its class.
[Example 1:
struct X { X(int); X(const char*, int = 0); X(int, int);};
void f(X arg) { X a = 1; // a = X(1) X b = "Jessie"; // b = X("Jessie",0) a = 2; // a = X(2) f(3); // f(X(3)) f({1, 2}); // f(X(1,2))} â end example]
[Note 1:
An explicit constructor constructs objects just like non-explicit constructors, but does so only where the direct-initialization syntax ([dcl.init]) or where casts ([expr.static.cast], [expr.cast]) are explicitly used; see also [over.match.copy].
A default constructor can be an explicit constructor; such a constructor will be used to perform default-initialization or value-initialization ([dcl.init]).
[Example 2: struct Z {explicit Z(); explicit Z(int); explicit Z(int, int);};
Z a; // OK, default-initialization performed Z b{}; // OK, direct initialization syntax used Z c = {}; // error: copy-list-initialization Z a1 = 1; // error: no implicit conversion Z a3 = Z(1); // OK, direct initialization syntax used Z a2(1); // OK, direct initialization syntax used Z* p = new Z(1); // OK, direct initialization syntax used Z a4 = (Z)1; // OK, explicit cast used Z a5 = static_cast(1); // OK, explicit cast used Z a6 = { 3, 4 }; // error: no implicit conversion â end example]
â end note]