Question

I have a char array. I take its address and pass it to a function which accepts a double char pointer:

char result[1024+1];
memset(result, 0, sizeof(result));
executeGetQuery(query, &(result));

Function definition: int executeGetQuery(char * query, char ** queryResultData)

I get this compile time error

warning: argument #2 is incompatible with prototype:
prototype: pointer to pointer to char : line 1531
argument : pointer to array[1025] of char

I’ve always passed arrays as pointers in C before. Why am I getting this error? Is my compiler to blame?

EDIT: What is the fix?
EDIT2: I want the function to write something to the result array which is why I am passing a char** instead of char*. What is then another way, the way, to have a function write to a param which I pass in?

Answer 1

What is the fix?

In this case (you don’t need the char **) use char * both in the prototype and the calling code

int executeGetQuery(char *query, char *queryResultData);
executeGetQuery(query, result);

I’d also include a size argument for protecting against buffer overflows

int executeGetQuery(char *query, char *queryResultData, size_t len);
executeGetQuery(query, result, sizeof result);

---

Edit:

to change the contents of the array do something like

int executeGetQuery(char *query, char *queryResultData, size_t len) {
    queryResultData[0] = 'H';  /* changing */
    queryResultData[1] = 'i';  /* the contents */
    queryResultData[2] = '\0'; /* of the array */
}

You can see the change in the calling function

executeGetQuery(NULL, result, sizeof result);
printf("result is now %s\n", result); /* should print "Hi" */