"warning: multi-line character constant"

The code below works but gives the warning "warning: multi-line character constant" for each character constant I have in the switch-case statement.

Code:

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int GObject::configure(const ConfEl* conf){
        while(conf){
                switch(conf->item.id){
                case 'posx':
                        obj.pos.x = conf->data.i;
                        break;
                case 'posy':
                        obj.pos.y = conf->data.i;
                        break;
                case 'posz':
                        obj.pos.z = conf->data.i;
                        break;
                case 'flag':
                        flags = conf->data.i;
                        break;
                case 'obj3':
                        load3db(conf->data.str);
                        break;
                }
                conf = conf->next;
        }
        return 0;
}

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conf->item.id is an unsigned integer which represents 4 characters. The code above works as expected. Why do I get those warnings? What can I do to eliminate those warnings?

Thank you

How did you assign the integer item.id?
Some macro with a 4-character string?

You get the warning because it is usually a mistake to use multiple characters as a constant. I'm not quite sure how you go about avoiding the warning - execpt I prefer to use proper constants instead of 'xxxx' for integer values for portability reasons (endian-ness changes the values).

Which compiler are you using?

--
Mats

I'm using gcc. For the conf->item.id I want the id's of objects be "names" and integers at the same time. To create the 'id' I parse a file of "name=value" pairs and the first 4 letters are used.

the actual code:

Code:

---

/* n is of the form "name=value" or "name{"
 * copyName takes the "name" and puts it in i->id/name
 */
int copyName(ConfItem* i, char* n){
        int k;
        static char buf[32];
        /* Gets the "name" part of "name=value" and stores in buf */
        getIDPart(buf, n);
        /* check if the "name" part looks like a hexnumber e.g. "0x3434" */
        if(isHexStr(buf)){
                /* use id specified */
                sscanf(buf+2, "%x", &i->id);
        } else {
                /* if not use first 4 letters of "name" */
                i->id = 0;
                /* create id from first 4 letters */
                for(k = 0; k < 4; k++){
                        if(buf[k] == 0)
                                break;
                        /* i->name & i->id share a union: The next line is not portable its either (3-k) or (k)
                        * depending on endianess */
                        i->name[3-k] = buf[k];
                }
        }
        return 0;
}

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Any chance you wrote the error mesage down wrong here? None of those multi-character constants appear to go over multiple lines. "multi-character" would make more sense.
You may have to resort to #prgamas or other compiler specific methods to suppress this warning. Or perhaps just an explicit cast will help?

I don't think how the values were assigned to id is relevent to the error, but Salem is probably looking for a way to avoid using them entirely.

I was thinking along these lines

Code:

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#define MAKEID(x)  ( (x[0]<<24) | (x[1]<<16) | (x[2]<<8) | (x[3]) )

// Then you can do
i->id = MAKEID(buf);
// You might want to make sure buf is padded with \0 out to 4 characters

// You can also do
case MAKEID("posx"):

---

Yes I made a mistake copying the error, it is "multi-character". Putting the MAKEID macro into the "case" statement gives

Code:

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                case MAKEID("posx"): ./* Line 8 */
                        obj.pos.x = conf->data.i;
                        break;

// gobject.cpp:8: error: an array reference cannot appear in a constant-expression

---

It doesn't seem like gcc pre-calculates the values. Perhaps a perl-script to replace MAKEID's with pre-calculate values? That will start to make my work look "magical" to others though.

Or you give it four parameters with individual character constants.

Code:

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MAKEID('p', 'o', 's', 'x')

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