gcc compilation error on simple short int function call with flag -Werror=traditional-conversion

Question

Compiling this C program with gcc 11.4.0 and -Werror=traditional-conversion raises an error:

short int f(short int x);

short int f(short int x) {
    return x;
}

int main(void)
{
    short int a = 0;
    f(a);

    return 0;
}

error: passing argument 1 of ‘f’ with different width due to prototype

Assuming that I can't change the function's signature because it comes from a library, is there a way to change the calling code to make the error go away?

I did try several kind of integer types for the a variable but to no avail. I would not expect the error to appear because the variable and the function's parameter prototype type are the same (short int). It looks to me like a false positive but it may be related to some implicit default promotion. I would rather find a solution that doesn't make me remove this compilation flag.

Just don't enable that error. The thing it's complaining about is not really an error. — Barmar
– Barmar, Commented Sep 20, 2024 at 22:48
It's warning about something that would be a problem if you didn't have a function prototype in scope (because short int would be converted to int by default promotions). But since you do, it's not a problem. — Barmar
– Barmar, Commented Sep 20, 2024 at 22:49
IMHO that error is useless and it will produce lots of false positives like that. The purpose seems to be to ensure compatibility with K&R C, which is not something you should worry about over 40 years later. — Barmar
– Barmar, Commented Sep 20, 2024 at 22:56

dbush · Accepted Answer · 2024-09-20 22:49:54Z

2

If you have no choice but to compile with this flag, you can disable it for a few lines using a pragma:

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wtraditional-conversion"
    f(a);
#pragma GCC diagnostic pop

answered Sep 20, 2024 at 22:49

dbush

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2 Comments

Barmar Over a year ago

This will get quite tedious if they have to put this pragma around every call to functions that take an argument smaller than int.

jarufi Over a year ago

I was hoping there would exists a code syntax to help the compiler see that this was a false positive, but if it has to be a compiler ignore comment, so be it. The method I was trying to call is htons. Thanks!

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