What is the type of T?
In the code below:
template<typename T>
struct X {};
int main()
{
X<int()> x; // what is the type of T ?
}
What is the type of T? I saw something 开发者_如何学编程like this in the boost
sources.
Consider the function int func()
. It has a function type int(void)
. It can be implicitly converted to pointer type as the C++ Standard says in 4.3/1, but it this case there's no need in such conversion, so T
has the function type int(void)
, not a pointer to it.
Here is what I did. Though the output of code below is implementation specific, many times it gives a good hint into the type of T that we are dealing with.
template<typename T>
struct X {
X(){
cout << typeid(T).name();
}
};
int main()
{
X<int()> x; // what is the type of T ?
cout << typeid(int()).name() << endl;
}
The output on VC++ is
int __cdecl(void)
int __cdecl(void)
The type of T
is a function that takes no parameters and returns int
, as in:
template<typename T>
struct X {};
int foo()
{
return 42;
}
int main()
{
X<int()> x; // what is the type of T ?
typedef int(foo_ptr)();
X<foo_ptr> x2;
return 0;
}
T
in x
and x2
are the same type.
精彩评论