How can I change the memory address of char*?

Question

I am dealing with a problem that I cannot get abs_path and query arrays filled with a data I am passing to them inside of the function parse. Inside this function logic seems to be correct, I have debugged it and both of the arrays are filled with a correct data. I know that I am not passing a pointer to arrays (char**) in the parameters due to a condition that function's parameters cannot be changed. Any other advice on solving this problem?

#define LimitRequestLine 8190
char abs_path[LimitRequestLine + 1];
char query[LimitRequestLine + 1];

bool parse(const char* line, char* abs_path, char* query)
{
    char* method = "GET ";
    char* valid_http = "HTTP/1.1";
    int index, method_size;
    char abs_path_line[LimitRequestLine + 1];
    char query_line[LimitRequestLine + 1];
    int abs_path_index;

    if(strstr(line, "HTTP/")!=NULL && strstr(line, valid_http) == NULL) {
        error(505);
        return false;
    }

    //make sure that our method is GET
    for(index = 0, method_size = strlen(method); index<method_size; index++) {
        if(line[index] != method[index]) {
            error(405);
            return false; 
        }
    }

    //check if request-target starts with '/'
    if(line[index]!='/') {
            error(501);
            return false; 
    }

    for(abs_path_index = 0; index < strlen(line); index++) {

       //if there is a quotation mark, then we have a query in request-target
       if(line[index] == '?') {
        index++;
        int query_index;

        for(query_index = 0; line[index]!=' '; index++) {

            //check if there is quote mark in query
            if(line[index] == '"') {
                error(400);
                return false; 
            }

            query_line[query_index] = line[index];
            query_index++;
        }

            query_line[query_index] = '\0';
       }

       //assuming that we have not found any '?' mark for query.
       if(strstr(line, "?") == NULL) {
          query_line[0] = '\0'; 
       }

       if(line[index] == ' ') {

           int temp = index;
           index++;

           /*After the space there should be a valid http, if it is not found,
           then there is/are spaces in our request-line which is incorrect*/
           for(int i=0; i<strlen(valid_http); i++) {
               if(line[index] != valid_http[i]) {
                   error(400);
                   return false; 
               }
               index++;
           }

           index = temp;
           break;
       }

       //check if there is quote mark in abs_path
        if(line[index] == '"') {
            error(400);
            return false; 
        }

        abs_path_line[abs_path_index] += line[index];
        abs_path_index++;
    }

    abs_path_line[abs_path_index] += '\0';

    abs_path = abs_path_line;
    abs_path += '\0';
    query = query_line;
    printf("abs path is %s\n", abs_path);
    printf("query is %s\n", query);


    return true;
}

Answer 1

The problem is this:

query = query_line;

char *query means you are passed a pointer. It's just a number like any other number. Think of it this way.

void set_number(int number) {
    number = 6;
}

Do you expect this to do anything? Nope. Same thing with query = query_line .

Instead, query points at a hunk of memory. You need to copy query_line into the memory that query points at and hope there's enough allocated space.

strncpy(query, query_line, LimitRequestLine);

---

Functions that require the caller to allocate memory are memory problems waiting to happen. Instead of fixing this one I would recommend...

1. Writing a new function with a better signature, maybe returning a struct.
2. Implement this old function as a wrapper around the new one.
3. Deprecating this function.

---

Note that the query in your function is not the same as the query declared outside the function.