Question

Please help me understand what I am doing wrong with my double pointer arithmetic. I know I clearly doing something incorrect but what? Look at the line where I marked, “bad pointer”. My intuition told me that this should work, but I guess not. Programmed in C.

/*
 *This function searches for prefixes within the string array.
 *@param stringArray array containing strings
 *@param searchPrefix a string or characters to search for at beginning of string
 *@return void
 */
 void prefixSearch(char* stringArray[SIZE], char* searchPrefix){
int count = strlength(searchPrefix);//size of the prefix search
while(count > 0){
    if(**stringArray == *searchPrefix){
        printf("%c match %c\n", **stringArray, *searchPrefix);
        **stringArray++;//want to move to next character, instead get bad pointer.
        *searchPrefix++;//moves to next char
    }else{
        stringArray++;//no match, go to next string
    }
    count--;//decrement
}

}

Answer 1

The * and ++ operators have the same precedence, and right-to-left associativity, so the line that’s not working parses like this:

*(*(stringArray++));

I don’t actually understand your code, but that can’t be what you intended since the dereference operators have no effect. Presumably you wanted this instead:

(**stringArray)++;