Prevent assignment of a type in C

Question

Given a C function:

void f(T x, T y) {
    x = y;
}

I want to make sure that all instances of T assignments will fail. So far, the best solution I have is something like:

#define T const void *

is there a better solution? (Ideally I would like T to be defined as some kind of a non-assignable opaque record pointer type).

It's unclear what it is that you want. Do you want `x = y` to generate a compilation error ? Something else ? Do you want to only impact the `f` function ? Or should this be some global behaviour ? How does using `const void*` achieve that ? — Sander De Dycker, Jul 15 '13 at 11:33

score 3 · Accepted Answer · answered Jul 15 '13 at 11:29

3

typedef is more suitable here.

For immutable data: typedef const void * T;

For immutable pointer: typedef void * const T;

answered Jul 15 '13 at 11:29

SomeWittyUsername

@tohava either you want the pointer to be const or the pointed data. These are 2 different things. the way you used the `#define` you need the first. – SomeWittyUsername Jul 15 '13 at 11:33
I added a clarification, sorry for my mistake. – tohava Jul 15 '13 at 11:37

score 0 · Answer 2 · answered Jul 15 '13 at 11:37

0

I made a dumb mistake. Apparently,

typedef const int T

or

typedef void * const T

work fine for preventing the assignment.

answered Jul 15 '13 at 11:37

tohava

2 Answers2