Wednesday, October 5, 2022

[SOLVED] Is there a GCC warning that can indicate any type change?

Issue

I have the following typedefs in my code:

#define FOO_OFF 0
#define FOO_ON 1
typedef uint8_t foo;

#define BAR_NO  0
#define BAR_YES 1
#define BAR_UNKNOWN 255
typedef uint8_t bar;

Those two types, although they have the same underlying type, they do not carry the same information.

And actually, I would like to get a warning if anyone in the code does something like:

foo foovar = FOO_OFF;


void get_bar(bar *outvar)
{
    // assigning the bar variable a foo variable content
    *outvar = foovar;
}

I could not find any such warning option in gcc, I have come accross -Wconversion but this warns only if there is a chance of losing information which is not the case in my example.

Does anyone know if there is something I can do? Obviously, it should be possible to cast when a type change is really needed.


Solution

Short answer is no, you can't do this. typedef declare an alias, not a new type, so any compiler respecting the standard cannot have the feature you want right now.

However, you can achieve it, by introducing a new type, using an enum, or a struct.

If you're in C, you will be able to cast from one enum to the other easily.

Because the address of the first element of a struct is also the address of a struct, you would be able to cast it from and to int8 or another struct, by casting the struct address, then de-referencing the pointer with it's new type. (*((dest_type *)&value))



Answered By - Phantomas
Answer Checked By - Pedro (WPSolving Volunteer)
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