cURL trouble with getting post response

[oceanman666]

I'm trying to create a basic login program that's connected to server but when I try to save the response from a post request to a variable I wont get a response at all but if I don't try to save it I do get a response, I'm not really sure what I'm doing wrong, any help would be appreciated, cheers.

    int post(string str1, string str2, string str3) {
        
        string query = "user=" + str1 + "&pass=" + str2;
        
        CURL *curl;
        CURLcode res;
        curl = curl_easy_init();
        
        if (curl) {
        
            curl_easy_setopt(curl, CURLOPT_URL, "mywebsite");
            curl_easy_setopt(curl, CURLOPT_POSTFIELDS, query.c_str());
            
            // when i comment out these 2 lines I get a response otherwise I don't
            curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_to_string);
            curl_easy_setopt(curl, CURLOPT_WRITEDATA, &str3);
            
            res = curl_easy_perform(curl);
            curl_easy_cleanup(curl);
        }

        curl_global_cleanup();

        return 0;
    }

Write to string

    size_t write_to_string(void *ptr, size_t size, size_t count, void *stream) {
        ((string*)stream)->append((char*)ptr, 0, size*count);
        return size*count;
    }