CURLOPT_TRAILERDATA(3)

💅 CURLOPT_TRAILERDATA 💅

okay so bestie, welcome to the CURLOPT_TRAILERDATA page from the libcurl Library Functions Manual — yes it's a mouthful, we're getting through it together 🫶

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✨ NAME ✨

CURLOPT_TRAILERDATA — the pointer that gets passed to your trailing headers callback. that's it, that's the whole vibe 🎀

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🌸 SYNOPSIS 🌸

#include <curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_TRAILERDATA, void *userdata);

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🦋 DESCRIPTION 🦋

so this is the data pointer, right? and the whole point of it is that it gets handed off to the HTTP trailer callback function. like, you set it here, and when that callback fires, boom, there's your pointer waiting for you. it's giving "hold this for me" energy 💅 no cap.

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⭐ DEFAULT ⭐

NULL

literally nothing. empty. a clean slate ✨

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🌈 PROTOCOLS 🌈

this functionality affects http only. http girlies only, sorry to everyone else 💀

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🍓 EXAMPLE 🍓

struct MyData {
  void *custom;
};

int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    struct MyData data;
    curl_easy_setopt(curl, CURLOPT_TRAILERDATA, &data);
  }
}

see how &data just gets plopped in there? iconic. you're passing your own little struct along for the ride 👑

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💜 AVAILABILITY 💜

added in curl 7.64.0 — so if you're on anything older, sorry bestie, time to upgrade 😭

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🔥 RETURN VALUE 🔥

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

CURLE_OK (0) means everything was OK — slay 💖 — and non-zero means an error occurred. for the full lore on those, see libcurl-errors(3). iykyk.

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👑 SEE ALSO 👑

• CURLOPT_TRAILERFUNCTION(3)
• CURLOPT_WRITEFUNCTION(3)

if TRAILERDATA is the data, TRAILERFUNCTION is the callback it partners with — they're a matched set, fr fr 🫶

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ngl this one's short but it eats. set the pointer, let the callback do its thing, periodt 💅

and that's the page!! brought to you by libcurl, dated 2026-10-12, and yes the footer says CURLOPT_TRAILERDATA(3) again because manpages love a little encore 🌸 bye bestie, go write some trailers 🧚✨