c++ - C++中的两个复制构造函数调用有什么区别？

Question

看下面的代码:

class Foo    
{ 
public:  
    Foo(){}  
    explicit Foo(const Foo &){}  
};  
int main()  
{  
    Foo foo1;  
    Foo foo2(foo1);  
    Foo foo3 = foo1; //can not compile    
    return 0;  
}  

为什么Foo foo3 = foo1;编译不通过，这两种拷贝构造函数调用有什么区别？
ps:我的编译工具是GCC4.8.2

Answer 1

Foo foo2(foo1); 是 direct initialization . Foo foo3 = foo1; 是 copy initialization .它们的区别在于

Copy-initialization is less permissive than direct-initialization: explicit constructors are not converting constructors and are not considered for copy-initialization.

Foo 的复制构造函数声明为显式，在复制初始化时不考虑。