c - Array of pointer to functions, having different number of arguments

Question

I am making a simple scheduler that executes functions contained in a FIFO queue.

Those functions have a same return type int, but have different number of int arguments.

I tried to implement it this way, but it does not seem to work. The compiler forbids conversion between int(*)() , int(*)(int), int(*)(int, int), or to any of those sort. (Arduino Sketch compiler)

Is there a way to solve this problem, or could you recommend a better way around? Thanks!

My code:

typedef int (*fnptr)(); // Tried this!

int foo(int var) {
    return 0;
}

int main() {
    fnptr fp = &foo; // error: invalid conversion from 
                     // 'int (*)(int)' to 'int (*)()' 
                     // [-fpermissive]
    return 0;
}

Also, please be aware, using a mismatched function pointer to call a function can invoke UB. — Sourav Ghosh
– Sourav Ghosh, Commented Jan 16, 2016 at 18:02
@SouravGhosh Yup, it throws the same error. 'fnptr fp = &foo()' also makes the same error. — upoque
– upoque, Commented Jan 16, 2016 at 18:04
I believe your code works in C89. C99 introduced the "limitation" of "remove implicit int". — pmg
– pmg, Commented Jan 16, 2016 at 18:14

unwind · Accepted Answer · 2017-04-12 12:29:13Z

0

You can cast:

fnptr fp = reinterpret_cast<fnptr>(foo);

The ()s are the "function call operator", adding them makes no sense at all in this situation, it changes the expression from "take the address of this function" to "take the address of this function's return value".

Note that aboev I don't even include the &, this is because the name of a function acts pretty much like a function pointer so it's already an address.

answered Apr 12, 2017 at 12:29

unwind

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