cURL C++ Example

curl_example.cpp

#include <iostream>
#include <string>
#include <curl/curl.h>


static size_t WriteCallback(void *contents, size_t size, size_t nmemb, void *userp)
{
    ((std::string*)userp)->append((char*)contents, size * nmemb);
    return size * nmemb;
}

int main(void)
{
  CURL *curl;
  CURLcode res;
  std::string readBuffer;

  curl = curl_easy_init();
  if(curl) {
    curl_easy_setopt(curl, CURLOPT_URL, "http://www.google.com");
    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, WriteCallback);
    curl_easy_setopt(curl, CURLOPT_WRITEDATA, &readBuffer);
    res = curl_easy_perform(curl);
    curl_easy_cleanup(curl);

    std::cout << readBuffer << std::endl;
  }
  return 0;
}

Works perfectly

guys i dont know how to integrate my project can you halp me ?

Build started...
1>------ Build started: Project: cmk, Configuration: Release Win32 ------
1>cmk.cpp
1>cmk.obj : error LNK2001: unresolved external symbol _curl_easy_perform
1>cmk.obj : error LNK2001: unresolved external symbol _curl_easy_init
1>cmk.obj : error LNK2001: unresolved external symbol _curl_easy_strerror
1>cmk.obj : error LNK2001: unresolved external symbol _curl_easy_cleanup
1>cmk.obj : error LNK2001: unresolved external symbol _curl_easy_setopt
1>C:\Users\Mustafa_Owner\source\repos\cmk\Release\cmk.exe : fatal error LNK1120: 5 unresolved externals
1>Done building project "cmk.vcxproj" -- FAILED.
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
========== Elapsed 00:01,275 ==========

main.cpp - > \n
#include
#include <curl/curl.h>

int main()
{
CURL* curl;
CURLcode res;

curl = curl_easy_init();
if (curl) {
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");

    /* Forcing HTTP/3 will make the connection fail if the server is not
       accessible over QUIC + HTTP/3 on the given host and port.
       Consider using CURLOPT_ALTSVC instead! */
    curl_easy_setopt(curl, CURLOPT_HTTP_VERSION, (long)CURL_HTTP_VERSION_3);

    /* Perform the request, res will get the return code */
    res = curl_easy_perform(curl);
    /* Check for errors */
    if (res != CURLE_OK)
        fprintf(stderr, "curl_easy_perform() failed: %s\n",
            curl_easy_strerror(res));

    /* always cleanup */
    curl_easy_cleanup(curl);
}

}

@hasirciogli

1. It looks like you did not include the -lcurl library when you compiled, hence the "unresolved external symbol" errors.
2. https://example.com does not support --http3, yet; you could test this using any HTTP/3 verifier.
   Try using any of the HTTP/3 supported websites, some are mentioned here.
3. I compiled and executed your code using https://quic.tech but received a curl_easy_perform() failed: SSL connect error error.
   Most probably because I don't have the OpenSSL libraries installed, and this is expected.
   But the code itself is executing fine.

#include <curl/curl.h>

int main()
{
	CURL* curl;
	CURLcode res;
	curl = curl_easy_init();
	if (curl)
	{
		curl_easy_setopt(curl, CURLOPT_URL, "https://quic.tech");
		curl_easy_setopt(curl, CURLOPT_HTTP_VERSION, (long)CURL_HTTP_VERSION_3);
		res = curl_easy_perform(curl);
		if (res != CURLE_OK)
			fprintf(stderr, "curl_easy_perform() failed: %s\n", curl_easy_strerror(res));
		
		curl_easy_cleanup(curl);
	}
}

Hope that helps :)

I developed a client which is receiving data from server occasionally. But when I receive first data, then program exists. I tried while loop like windows message loop, but it gives me last data.

How can I stay in program so that I can receive more messages from server.

@alghanmi Hi!

First off, thank you for sharing your code example! It was incredibly helpful for getting me started quickly. However, I wanted to point out a couple of discrepancies that I noticed:

1. Missing global initialization:
   The libcurl documentation recommends using curl_global_init() at the beginning of the program to set up the necessary environment for curl operations. See "Global preparation" section:
   - https://curl.se/libcurl/c/libcurl-tutorial.html
2. Callback prototype mismatch:
   The prototype for the callback function seems to be inconsistent with the one documented on the official libcurl site. The prototype for this callback function is described here:
   - https://curl.se/libcurl/c/CURLOPT_WRITEFUNCTION.html

size_t write_callback(char *ptr, size_t size, size_t nmemb, void *userdata);

On a related note, I've created a more detailed setup documentation and added a simple example as well as a slightly more complex one that includes POST requests, which some may find useful:
- https://github.com/voidlib/cpp-curl-example

Thanks again for your contribution—it was a great starting point for me!

Best regards,
@voiduin

this was the best explanation