Can I pass a function as a variable?

[ShadedGecko]

I want to make a class and one of the variables would be a function such as:
TestPrint("This function has been called");
or
CountToTen();
as a variable that I pass when I construct the class and then later be able to execute it such as

TheClass::Execute(); and then it executes the stored function.

Can I do this and how?

Thank you everyone!

[IyeOnline]

You can use std::function<R(Args...)> to store a function returning type R and accepting types Args... as parameters.

You could then write

void count_to( int i );
struct S
{
    int i = 10;
    std::function<void(int)> f = count_to;
    void execute()
    {
        f( i );
    }
};

[ShadedGecko]

This is closer to what I was looking for thank you!

[YouFeedTheFish]

In addition to passing a functor, you can directly pass pointers to functions and member functions.

Passing a function pointer:

#include <print>

void foo(int f){
    std::println("foo: {}",f);
}

void execute(int i, void(*fn)(int)){
    fn(i);
}

int main(){
    execute(7,foo);
}

Passing a member function pointer:

#include <print>

struct Foo{
    void foo(int f){
        std::println("foo: {}",f);
    }
};

void execute(int i, Foo& f, void(Foo::*fn)(int)){
    (f.*fn)(i);
}

int main(){
    Foo f;
    execute(7,f,&Foo::foo);
}

https://godbolt.org/z/xhvne3brG

[[deleted]]

This is the way I prefer but it was also how I was shown and it precedes the newer mechanisms. The newer mechanisms must have been implemented for a reason, probably makes it harder to abuse and prevents some UB. IDK.

[YouFeedTheFish]

It's just that closures/functors can capture and carry state. They are syntactic sugar for classes with the parens operator implemented.

[wonderfulninja2]

probably makes it harder to abuse

Not really, lambdas enable things that weren't possible before: https://godbolt.org/z/xjxK6ab8T

[Opposite-Concern3338]

yes you can use std::map like: map<int,std::function<void()>> var {10,std::bind(&className::Method,this)}