内容简介：http://stackoverflow.com/questions/26788402/why-does-foo-invoke-foo0-instead-of-foo
可执行文件由clang 3.5.0和gcc 4.9.1从代码生成
#include <iostream>
struct Foo
{
Foo() { std::cout << "Foo()" << std::endl; }
Foo(int x) { std::cout << "Foo(int = " << x << ")" << std::endl; }
Foo(int x, int y) { std::cout << "Foo(int = " << x << ", int = " << y << ")" << std::endl; }
};
int main() // Output
{ // ---------------------
auto a = Foo(); // Foo()
auto b = Foo(1); // Foo(int = 1)
auto c = Foo(2, 3); // Foo(int = 2, int = 3)
auto d = Foo{}; // Foo()
auto e = Foo{1}; // Foo(int = 1)
auto f = Foo{2, 3}; // Foo(int = 2, int = 3)
auto g = Foo({}); // Foo(int = 0) <<< Why?
auto h = Foo({1}); // Foo(int = 1)
auto i = Foo({2, 3}); // Foo(int = 2, int = 3)
}
表现为评论.
从 cppreference: cpp/language/list initialization ：
06001
The effects of list initialization of an object of type T are:
If T
is an aggregate type, aggregate initialization is performed.
Otherwise, If the braced-init-list is empty and T
is a class type with a default constructor, value-initialization is performed.
06002
我得出结论,Foo({})应该调用默认构造函数.
这个bug在哪里？
默认构造函数仅适用于您使用一对大括号：
auto a = Foo(); // Foo()
auto b = Foo{}; // Foo()
Foo({})只会调用具有空列表的构造函数作为参数,copy-list-initialize任何构造函数的参数. [dcl.init] / 16：
If the destination type is a (possibly cv-qualified) class type:
— If
the initialization is direct-initialization […] constructors are considered. The applicable constructors
are enumerated (13.3.1.3), and the best one is chosen through overload
The constructor so selected is called to
initialize the object, with the initializer expression or
expression-list If no constructor applies, orthe overload resolution is ambiguous, the initialization is
ill-formed.
你有一个参数：空的braced-init-list.有一个列表初始化序列将{}转换为int,所以构造函数Foo(int)是通过重载分辨率来选择的.参数初始化为零,因为{}表示一个 value-intialization ,对于标量,这意味着一个 zero-initialization .
在cppreferences文档中也没有错误：对于(7)说明
7) in a functional cast expression or other direct-initialization, with braced-init-list used as the constructor argument
这显然导致与上述引用相同的结果：使用(空)braced-init-list调用构造函数.
http://stackoverflow.com/questions/26788402/why-does-foo-invoke-foo0-instead-of-foo
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