模板+ Typedef C ++

Question

if we have a line of code :

typedef bool (*cmp_func)(int i0, int i1);

How to change this to :

typedef bool (*cmp_func)(T i0, T i1);

where T - typename ?

Answer 1

Since C++11:

template <typename T>
using cmp_func = bool (*)(T, T);

Answer 2

There is no template typedef, but you can have a typedef inside a template:

template <typename T> 
struct Foo {
    typedef bool (*cmp_func)(T i0, T i1);
};
int main() {
    Foo<int>::cmp_func f;
}

Or since C++11 you can do the same via type aliasing

template <typename T>
using cmp_func = bool(*)(T,T);

Also note that even though C++11 has type aliasing, this comes with some restrictions (in particular they cannot be specialized) and sometimes it is necessary to combine both approaches.