Returning a Function Pointer in C++

Question

Here is the code:

void (*)(const dpp::slashcommand_t &event) operator[](const std::string &index);

When I compile this, I get the following error message:

In file included from commands_controller.cpp:3,
                 from main.cpp:2:
commands_controller.h:28:12: error: expected unqualified-id before ‘)’ token
   28 |     void (*)(const dpp::slashcommand_t &event) operator[](const std::string &index);

Do you have any suggestion for how I can resolve this error?

The only sensible way to solve this is to create a type alias for your function pointer. I believe it is possible without one, but the syntax is tricky. — john
– john, Commented Dec 14, 2022 at 18:45
I've tried with type alias. It was " typedef void( * return_func)(const dpp::slashcommand_t &event)". It gave the error: "typedef does not define a type". By the way @tkausi, it is an operator overloading. — AdriaNn01
– AdriaNn01, Commented Dec 14, 2022 at 18:49
std::function (part of modern c++ for a while now) might save you some trouble — Pierre Baret
– Pierre Baret, Commented Dec 14, 2022 at 18:58
@PierreBaret -- indeed, but at the cost of some overhead. This is not it's primary use. — Pete Becker
– Pete Becker, Commented Dec 14, 2022 at 18:58

Mooing Duck · Accepted Answer · 2022-12-14 18:47:40Z

12

When dealing with function pointers, use typdefs. The correct non-typedef syntax is:

void (*operator[](const std::string &index))(const dpp::slashcommand_t &event)

https://coliru.stacked-crooked.com/a/4eabda845ac15a54

Obviously, this is completely insane.

So instead, always use a typedef or alias:

using slash_fn_ptr = void (*)(const dpp::slashcommand_t &event);
slash_fn_ptr operator[](const std::string &index);

https://coliru.stacked-crooked.com/a/fd96b9918b1526b7

answered Dec 14, 2022 at 18:47

Mooing Duck

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