explicit specifier

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Specifies constructors and (since C++11) conversion operators that don't allow implicit conversions

[edit] Syntax


explicit class_name ( params )

explicit operator type ( ) (since C++11)

[edit] Example

struct A
{
    A ( int ) {}
 
    operator int() const { return 0; }
};
 
struct B
{
    explicit B(int) {}
    explicit operator int() const { return 0; }
};
 
int main()
{
    // A is has no explicit ctor / conversion, everything is fine
    A a1 = 1;
    A a2 ( 2 );
    int na1 = a1;
    int na2 = int ( a1 );
 
    B b1 = 1; // Wrong: implicit conversion from int to B
    B b2 ( 2 ); // OK: explicit constructor call
    int nb1 = b1; // Wrong: implicit conversion from B to int
    int nb2 = int ( b1 ); // OK: explicit cast
}