What does this C syntax do: iVar = (*DAT)(param_2,PTR_s);

Question

i am quite new to reverse engineering and using Ghidra. Recently i have decompiled some arduino code. When i was looking at the decompiled code i noticed the following line.

iVar = (*DAT)(param_2,PTR_s);

I have cut of some parts of the variables. But i really wonder what this piece of code is doing. It is supposed to be decompiled c code. I have worked a bit with C, 2 years ago, but i cannot figure out what is happening here. PTR_s is supposed to be a pointer to a string and param_2 is a byte*. Havent figured out what *DAT exactly is.

`DAT` is probably a pointer to a function which is being called here. — Eugene Sh., Jun 04 '21 at 19:49
It is a reference to several functions, which made it weird for me to understand — Hakan, Jun 04 '21 at 19:51
Some reading on [C function pointers](https://stackoverflow.com/questions/840501/how-do-function-pointers-in-c-work) — Chris, Jun 04 '21 at 19:53
Ah thanks i understand the syntax now. *DAT is a function pointer and the two values in the second parentheses are the parameters for the function. — Hakan, Jun 04 '21 at 19:54

unwind · Answer 1 · 2021-06-04T19:58:52.040

2

DAT is a pointer to a function, which is being (needlessly) deferenced, then called with the two arguments param_2 and PTR_s. The return value is then stored in the variable iVar.

Here is a very short and rather silly sample program in which the above statement appears:

#include <stdio.h>

static int add(int x, int y)
{
    return x + y;
}

int main(void)
{
    int (*DAT)(int, int) = add;
    const int param_2 = 17;
    const int PTR_s = 25;
    const int iVar = (*DAT)(param_2, PTR_s);
    printf("I got %d\n", iVar);
    return 0;
}

It prints the sum of 17 and 25, i.e. the output is:

I got 42

edited Jun 04 '21 at 19:58

answered Jun 04 '21 at 19:55

unwind

391,730
64
469
606

1

`DAT` could be a pointer to a pointer to a function, in that case the dereferencing is justified? – Eugene Sh. Jun 04 '21 at 19:56
@EugeneSh. Sure, that 's true. Good point, I guess, and impossible to tell without further context. – unwind Jun 04 '21 at 19:59

What does this C syntax do: iVar = (*DAT)(param_2,PTR_s);

1 Answers1