explicit关键字的作用.doc

谈谈explicit关键字
2004-08-19 20:35 16677人阅读 评论(7) 收藏 举报
今天看到公司的代码内有大量的explicit关键字,但是老版的MSDN内例子并不完善,实在是不明白,最终从网上一篇文章内找到了答案::
// Copy From MSDN
This keyword is a declaration specifier that can only be applied to in-class constructor declarations. An explicit constructor cannot take part in implicit conversions. It can only be used to explicitly construct an object.
The following program will fail to compile because of the explicit keyword. To resolve the error, remove the explicit keywords and adjust the code in g.
//
// compile with: /EHsc
#include
class C
{
public:
int i;
explicit C(const C&) // an explicit copy constructor
{
printf("/nin the copy constructor");
}
explicit C(int i ) // an explicit constructor
{
printf("/nin the constructor");
}
C()
{
i = 0;
}
};
class C2
{
public:
int i;
explicit C2(int i ) // an explicit constructor
{
}
};
C f(C c)
{ // C2558
= 2;
return c; // first call to copy constructor
}
void f2(C2)
{
}
void g(int i)
{
f2(i); // C2558
// try the following line instead
// f2(C2(i));
}
int main()
{
C c, d;
d = f(c); // c is copied
}
Note   explicit on a constructor with multiple arguments has no effect, since such const