Heap increase - Curl HTTP request - c++

Question

I am currently using CURL library, I tried a simple example and I noticed that the heap memory increases every time I make a request. This is a very important problem, especially when you are trying to use multithread.
Does anyone know the problem?
static int Swriter(char *data, size_t size, size_t nmemb, std::string *writerData)
{
if(writerData == NULL)
return 0;
writerData->append(data, size*nmemb);
return size * nmemb;
}
static void RequestReadJson(std::string url, std::string &content)
{
CURL *curl = curl_easy_init();
if (curl) {
curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, Swriter);
curl_easy_setopt(curl, CURLOPT_WRITEDATA, &content);
curl_easy_perform(curl);
curl_easy_cleanup(curl);
}
}
int main(int argc, wchar_t* argv[]) {
curl_global_init(CURL_GLOBAL_DEFAULT);
std::string content;
std::string url("www.google.com");
for(int i=0;i<300;i++)
RequestReadJson(url, content); //Heap increase
curl_global_cleanup();
}
Heap increase

Answer 1

You append the new downloaded content to the old, hence the heap increase:
curl_easy_setopt(curl, CURLOPT_WRITEDATA, &content);
which leads to:
writerData->append(data, size*nmemb);
You'd better return a fresh string:
static std::string RequestReadJson(std::string url)
{
std::string content;
CURL *curl = curl_easy_init();
if (curl) {
curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, Swriter);
curl_easy_setopt(curl, CURLOPT_WRITEDATA, &content);
curl_easy_perform(curl);
curl_easy_cleanup(curl);
}
return content;
}