<分区>
我在 Cpp Quiz 看到了一个代码[问题 #38]
#include <iostream>
struct Foo
{
Foo(int d) : x(d) {}
int x;
};
int main()
{
double x = 3.14;
Foo f( int(x) );
std::cout << f.x << std::endl;
return 0;
}
据说这段代码格式错误，因为 Foo f( int(x) ); 将被视为函数声明而不是 Foo< 类型的对象声明.
据我所知，这是“最令人烦恼的解析”的一个实例。我的问题是语句 Foo f( int(x) ); 中的语法 int(x) 是什么意思？到目前为止，我只看到函数声明如下:
Foo f( int ); 和
Foo f( int x );
它和Foo f( int x ); 一样吗？
最佳答案
what does this syntax
int(x)in the statementFoo f( int(x) );mean?
x 两边的括号是多余的，将被忽略。所以int(x)和这里的int x是一样的，意思是一个名为x的参数，类型是int .
Is it the same as
Foo f( int x );?
是的。 Foo f( int(x) );，是一个名为f的函数声明，返回Foo，接受一个名为的参数x 类型为 int。
这是标准的解释。 [dcl.ambig.res]/1 :
(强调我的)
The ambiguity arising from the similarity between a function-style cast and a declaration mentioned in [stmt.ambig] can also occur in the context of a declaration. In that context, the choice is between a function declaration with a redundant set of parentheses around a parameter name and an object declaration with a function-style cast as the initializer. Just as for the ambiguities mentioned in [stmt.ambig], the resolution is to consider any construct that could possibly be a declaration.
Note: A declaration can be explicitly disambiguated by adding parentheses around the argument. The ambiguity can be avoided by use of copy-initialization or list-initialization syntax, or by use of a non-function-style cast.
struct S { S(int); }; void foo(double a) { S w(int(a)); // function declaration S x(int()); // function declaration S y((int(a))); // object declaration S y((int)a); // object declaration S z = int(a); // object declaration }
因此，int(x) 将被视为(参数的)声明而不是函数样式转换。
关于c++ - 最烦人的解析，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/38951362/