Trying to achieve generics without using pointers in C.

[Gat Pelsinger]

I am coding an array list in C. In my add function, it accepts a void pointer called element currently. The reason it is a void pointer is because I don't know what type is the element going to be. But if I do so, then when calling the function, I always have to first create a new variable and pass it's value by reference, which is not ideal. And if use a normal variable instead of a pointer, then I cannot use void and it has to be tied to a specific data type.

[Eigenvektor]

Any reason you're not using a language that supports generics out of the box, like C++?

 

The whole idea behind generics is to have type safety. Which requires language support. So even if you find a workaround for your issue, it's going to be an ugly hack since you lose type information.

[dcgreen2k]

Using void pointers is the standard way to implement generics in C. If you really don't want to use void pointers, then you could use macros like shown here: https://stackoverflow.com/questions/16522341/pseudo-generics-in-c

 

However, this generally isn't recommended. C++ has support for generics built in and will be much less of a headache to use.

[Gat Pelsinger]

@Eigenvektor @dcgreen2k

 

The reason I am using C is because I am just planning to actually learn and master it before hopping onto other languages. I am actually coding a custom array list for another program that I am programming, but I am keeping all the abstraction and independence so I can use it outside my program in other programs. So, can I code my array list in C++ and still make it compatible with the rest of my C program?

 

And to be honest, don't I just need 1 variable of that same type to be able use my Array List? For example when I first call my add function, I pass the value of say, char x[] = "12345" by reference. And the add function adds the element, and now doesn't even need my char x[]. So can I not use that same variable to change it's data and pass that to another call to the add function by reference?

[Eigenvektor]

18 minutes ago, Gat Pelsinger said:

So, can I code my array list in C++ and still make it compatible with the rest of my C program?

There are ways to mix C and C++, but you need to keep your code compatible with C, so "real" generics are out.

 

To make the code reusable, ideally you would turn that array list into a generic class (in C++) that can be instantiated and reused wherever needed (of course, if it wasn't for learning purposes you'd use std::list instead of rolling your own)

 

24 minutes ago, Gat Pelsinger said:

And to be honest, don't I just need 1 variable of that same type to be able use my Array List?

If your list creates a copy, then yes you can reuse your original variable. You just need to be careful if you're dealing with pointers. If the list stores a pointer instead and you change/reuse the value it is pointing to, then your list would now be pointing to the changed value instead.