cURL - put output into variable? - c

Question

I'm currently using this C code:
CURL *curl;
CURLcode res;
curl = curl_easy_init();
if (curl) {
curl_easy_setopt(curl, CURLOPT_URL, "http://my-domain.org/");
res = curl_easy_perform(curl);
curl_easy_cleanup(curl);
}
It prints the output on the console. How can I get the same output, but read it into, say, a string? (This is a probably a basic question, but I do not yet understand the libcurl API...)
Thanks for any help!
Mike

Answer 1

You need to pass a function and buffer to write it to buffer.
/* setting a callback function to return the data */
curl_easy_setopt(curl_handle, CURLOPT_WRITEFUNCTION, write_callback_func);
/* passing the pointer to the response as the callback parameter */
curl_easy_setopt(curl_handle, CURLOPT_WRITEDATA, &response);
/* the function to invoke as the data recieved */
size_t static write_callback_func(void *buffer,
size_t size,
size_t nmemb,
void *userp)
{
char **response_ptr = (char**)userp;
/* assuming the response is a string */
*response_ptr = strndup(buffer, (size_t)(size *nmemb));
}
Please take a look more info here.

Answer 2

you need a write callback function. I use this kind of function to read the response, error and be able to supply my own headers:
size_t write_data(void *ptr, size_t size, size_t nmemb, void *stream)
{
std::string buf = std::string(static_cast<char *>(ptr), size * nmemb);
std::stringstream *response = static_cast<std::stringstream *>(stream);
response->write(buf.c_str(), (std::streamsize)buf.size());
return size * nmemb;
}
bool CurlGet(
const std::string &url,
const std::vector<std::string> &headers,
std::stringstream &response,
std::string &error)
{
curl_global_init(CURL_GLOBAL_ALL);
curl_slist *headerlist = NULL;
std::vector<std::string>::const_iterator it;
for (it = headers.begin(); it < headers.end(); it++) {
headerlist = curl_slist_append(headerlist, it->c_str());
}
CURL *curl = curl_easy_init();
char ebuf[CURL_ERROR_SIZE];
curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
curl_easy_setopt(curl, CURLOPT_NOPROGRESS, 1);
curl_easy_setopt(curl, CURLOPT_ERRORBUFFER, ebuf);
curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data);
curl_easy_setopt(curl, CURLOPT_WRITEDATA, &response);
curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headerlist);
CURLcode res = curl_easy_perform(curl);
curl_easy_cleanup(curl);
curl_slist_free_all(headerlist);
if (res != CURLE_OK)
error = ebuf;
else
error.clear();
return res == CURLE_OK;
}

Answer 3

This can be done using
curl_easy_setopt(easyhandle, CURLOPT_WRITEFUNCTION, write_data);
which sets a callback function write_data which is a function with the signature
size_t write_data(void *buffer, size_t size, size_t nmemb, void *userp);
If you want userp be some internal struct you are using in your program, call
curl_easy_setopt(easyhandle, CURLOPT_WRITEDATA, &internal_struct);
to get the pointer to internal_struct passed to every call of write_data.

Answer 4

Hi i solve issue of return code 23 from call back function to return size from call back function.
see below code:
/* setting a callback function to return the data */
curl_easy_setopt(curl_handle, CURLOPT_WRITEFUNCTION, write_callback_func);
/* passing the pointer to the response as the callback parameter */
curl_easy_setopt(curl_handle, CURLOPT_WRITEDATA, &response);
/* the function to invoke as the data recieved */
size_t static write_callback_func(void *buffer,
size_t size,
size_t nmemb,
void *userp)
{
char **response_ptr = (char**)userp;
/* assuming the response is a string */
*response_ptr = strndup(buffer, (size_t)(size *nmemb));
return ((size_t)(size *nmemb));
//if you not send return value of size it will show you ERROR CODE 23return curl_easy_perform();
}

Answer 5

None of the other examples worked for me.
Here's what I eventually ended up doing:
size_t static curl_write(void *buffer, size_t size, size_t nmemb, void *userp)
{
userp += strlen(userp); // Skipping to first unpopulated char
memcpy(userp, buffer, nmemb); // Populating it.
return nmemb;
}
int GetCurl()
{
CURL *curl;
CURLcode res;
char *s = (char *) malloc(512);
curl = curl_easy_init();
if (curl)
{
curl_easy_setopt(curl, CURLOPT_URL, "http://www.google.com");
curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, curl_write);
curl_easy_setopt(curl, CURLOPT_WRITEDATA, s);
res = curl_easy_perform(curl);
curl_easy_cleanup(curl);
}
printf("GREAT SUCCESS!! Your string is %s\n", s);
}