C++ Finish Current task before moving on to the next - c++

Question

Im trying to find a way to download a file and have the program wait for the download to finish then move onto the next task which in this case would be checking to see if the file exist
#include <stdio.h>
#include <curl/curl.h>
#include <curl/easy.h>
#include <string>
#include <iostream>
#include <stdlib.h>
#include <fstream>
size_t write_data(void *ptr, size_t size, size_t nmemb, FILE *stream) {
size_t written = fwrite(ptr, size, nmemb, stream);
return written;
}
using namespace std;
int main(void) {
CURL *curl;
FILE *fp;
CURLcode res;
char *url = "http://199.91.153.180/y1plsynnb11g/e9g9mcd3fi5txov/UHC.jar";
char outfilename[FILENAME_MAX] = "UHC.jar";
curl = curl_easy_init();
if (curl) {
fp = fopen(outfilename,"wb");
curl_easy_setopt(curl, CURLOPT_URL, "http://199.91.153.180/y1plsynnb11g/e9g9mcd3fi5txov/UHC.jar");
curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data);
curl_easy_setopt(curl, CURLOPT_WRITEDATA, fp);
res = curl_easy_perform(curl);
/* always cleanup */
curl_easy_cleanup(curl);
fclose(fp);
}
ofstream launch;
launch.open("UHC.jar");
if (launch.is_open()){
cout<< "File Downloaded";
}
else {
cout << "Download Failed";
}
}

Answer 1

The HTTP request may have failed. Try adding error checking before /* always cleanup */
if (res)
cout << curl_easy_strerror(res) << endl;

Answer 2

I realized the return value of write_data is wrong. But it should have caused an error...
Anyway, please try:
size_t write_data(void *ptr, size_t size, size_t nmemb, FILE *stream) {
size_t written = fwrite(ptr, size, nmemb, stream);
return written * size;
}

Answer 3

I just realized what was wrong when it to check for the file existing using ofstream it was trying to write to it so it would make the file empty. Just changing it from ofsteam to fstream it works perfectly.