Explicit type conversion

cppreference Explicit type conversion

Converts between types using a combination of explicit and implicit conversions.

NOTE:

1、其中也会使用implicit conversion

Syntax

Returns a value of type new_type.

NOTE:

1、显然会构造一个新的object

( new_type ) expression	(1)
( new_type ( expression )	(2)
( new_type ( arg1, arg2, ... )	(3)
new_type ( )	(4)
new_type { arg1, arg2, ...(optional) }	(5)	C++11
template-name ( arg1, arg2, ...(optional) )	(6)	C++17
template-name { arg1, arg2, ...(optional) }	(7)	C++17

CppCoreGuidelines C.164: Avoid implicit conversion operators

struct S1 {
    string s;
    // ...
    operator char*() { return s.data(); }  // BAD, likely to cause surprises
};

struct S2 {
    string s;
    // ...
    explicit operator char*() { return s.data(); }
};

void f(S1 s1, S2 s2)
{
    char* x1 = s1;     // OK, but can cause surprises in many contexts
    char* x2 = s2;     // error (and that's usually a good thing)
    char* x3 = static_cast<char*>(s2); // we can be explicit (on your head be it)
}