Question

I’m trying to concatenate two chars and get a segmentation error on the line above return.
When I used char instead of char*, the (onechar-a + ‘A’) worked although I wasn’t trying to concatenate. If I leave this as char instead of char* I get warnings about casting.

char *carat;
carat = test_carat(ttyinfo.c_cc[VINTR]);
carat = test_carat(ttyinfo.c_cc[VINTR]);

char * test_carat(char onechar)
{
    if (onechar >= 32 || onechar !=127)
    {
        if (iscntrl(onechar))
        {
            char * returnString =  strcat((char*)'^',  (char*)(onechar - 1 + 'A'));
            return returnString;
        }
    }
}

Answer 1

That won’t work:

   strcat((char*)'^',  (char*)(onechar - 1 + 'A') ) 

You shouldn’t cast a character to a char pointer. The effect is that the character value (a value <= 255) will be used as address of the character pointer by strcat, this is why your program segfaults.

You can do that:

char * test_carat(char onechar)
{
    if (onechar >= 32 || onechar !=127)
    {
        if (iscntrl(onechar))
        {
            char * returnString = (char *)malloc(3);
            returnString[0] = '^';
            returnString[1] = (onechar - 1 + 'A');
            returnString[2] = '\0';
            return returnString;
        }
    }
    return NULL;
}