CURLOPT_XFERINFODATA(3)

✨ CURLOPT_XFERINFODATA(3) ✨

okay bestie, welcome to the libcurl manual page for CURLOPT_XFERINFODATA 💅 this one lives in the Library Functions Manual and honestly it's giving "small but mighty" — it's literally just a pointer, but it's the pointer that makes your progress callback not be lonely 🫶

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🌸 NAME 🌸

CURLOPT_XFERINFODATA — the pointer you pass to the progress callback 💖

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🎀 SYNOPSIS 🎀

#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_XFERINFODATA, void *pointer);

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🦋 DESCRIPTION 🦋

So here's the vibe: you pass in a pointer, and libcurl does not touch it. Not even a little. It just holds onto it and hands it right back to you as the first argument of the progress callback that you set with CURLOPT_XFERINFOFUNCTION(3). That's it. That's the whole job. iconic behavior honestly 👑

And plot twist — this is an alias for CURLOPT_PROGRESSDATA(3). same energy, different name, iykyk ✨

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💜 DEFAULT 💜

NULL

(no pointer, no problem — just nothing passed along 🙈)

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🌈 PROTOCOLS 🌈

This functionality affects all supported protocols 🌟 like, all of them, no cap.

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⭐ EXAMPLE ⭐

ok so imagine you've got a struct you wanna smuggle into your callback — here's how the girlies do it:

struct progress {
  char *private;
  size_t size;
};

static int progress_cb(void *clientp,
                       curl_off_t dltotal,
                       curl_off_t dlnow,
                       curl_off_t ultotal,
                       curl_off_t ulnow)
{
  struct progress *memory = clientp;
  printf("private ptr: %p\n", memory->private);
  /* use the values */

  return 0; /* all is good */
}

int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    struct progress data;

    /* pass struct to callback  */
    curl_easy_setopt(curl, CURLOPT_XFERINFODATA, &data);
    curl_easy_setopt(curl, CURLOPT_XFERINFOFUNCTION, progress_cb);
  }
}

see how clientp in the callback is literally your &data? that's the whole trick bestie 🧚 the pointer comes back to you completely untouched, main character energy fr fr 🔥

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🍓 AVAILABILITY 🍓

Added in curl 7.32.0 — so she's been around a minute 💅

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💀 RETURN VALUE 💀

curl_easy_setopt(3) returns a CURLcode indicating success or error.

CURLE_OK (0) means everything was OK 💚 non-zero means an error occurred 😭 — go check libcurl-errors(3) for the deets.

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👑 SEE ALSO 👑

• CURLOPT_NOPROGRESS(3)
• CURLOPT_VERBOSE(3)
• CURLOPT_XFERINFOFUNCTION(3)

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ok that's the whole page, go forth and pass pointers responsibly 🎀💖✨

ngl the actual manual says this page comes from libcurl and is dated 2026-10-12 — so yeah, that's the source, the version, and the date, all cute and accounted for 🫶🌈 slay.