Difficulty in understanding function-pointers in c++

Question

I am reading The C++ Programming Language by Bjarne Stroustrup. It somewhere uses using keyword to make function-pointer datatypes P1 and P2 like this:

using P1 = int(∗)(int∗);

using P2 = void(∗)(void);

But then it uses using keyword to make another function-pointer datatype:

using CFT = int(const void∗, const void∗);             -(1)

then it uses CFT to declare a function-pointer and passes it in some ssort function:

void ssort(void∗ base, siz e_t n, size_t sz, CFT cmp);

My question is if it is making a function-pointer datatype using "using" then shouldn't line-(1) be:

using CFT=int(*)(const void*, const void*);

rather than what it actually is?

which edition? Did you check the errata if they mention it there? — default
– default, Commented Feb 14, 2018 at 11:15
@Birbal: It's not in the book. If they knew the mistakes when they published the book, they wouldn't have made them. Google "the c++ programming language 4th edition errata". — Lightness Races in Orbit
– Lightness Races in Orbit, Commented Feb 14, 2018 at 11:20

Lightness Races in Orbit · Accepted Answer · 2018-02-14 11:24:43Z

5

In C and C++, the (*) is optional here.

Yes, this is confusing. It's an oddity regarding function pointer types.

It would have been better had the author stuck to one of the two possible syntaxen.

edited Feb 14, 2018 at 11:24

answered Feb 14, 2018 at 11:19

Lightness Races in Orbit

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6 Comments

Lightness Races in Orbit Over a year ago

Looking for a standard quote but can't actually find one. I think the types are different but end up being used the same.

bolov Over a year ago

they are not the same. It seems like in the context of function parameters are the same. godbolt.org/g/EhVV5Z

Lightness Races in Orbit Over a year ago

So what I just said then :)

bolov Over a year ago

yeah. It is very confusing. void call(F f) and void call2(F* f) have the same signature if F is a function type.

StoryTeller - Unslander Monica Over a year ago

It is indeed a distinct and incomplete function type. And it has its uses and oddities. I personally like that one may use the original CFT to make pointer semantics explicit, i.e. CFT*. Not to mention being able to use it with std::function, as you already mentioned.

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