CURLOPT_POSTFIELDSIZE_LARGE(3)

💖 CURLOPT_POSTFIELDSIZE_LARGE(3) 💖

okay so bestie, welcome to the Library Functions Manual, this is a curl_easy_setopt(3) page, and it's literally the one that tells libcurl how big your POST data is 🎀

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✨ NAME ✨

CURLOPT_POSTFIELDSIZE_LARGE — size of POST data pointed to. yeah that's it, that's the whole vibe 🌸

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✨ SYNOPSIS ✨

#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_POSTFIELDSIZE_LARGE,
                          curl_off_t size);

so you pass your handle, you pass the option, you pass a curl_off_t size, and you move on with your day 💅

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✨ DESCRIPTION ✨

Okay so picture this: you want to post some static data to the server, but you're like "girl, I am NOT letting libcurl run a strlen() on this to figure out the size." Same. And that's exactly when you use this option 🫶

When you use this option you can post fully binary data — which otherwise is likely to fail, and we do not want that for you, no ma'am 😭

And if this size is set to -1, libcurl just goes and uses strlen() to get the size — OR it relies on CURLOPT_READFUNCTION(3) (if you're using it) to signal the end of data. lowkey iconic of it to have options 💜

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✨ DEFAULT ✨

-1 — the default is literally just vibes and strlen() 🌈

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✨ PROTOCOLS ✨

This functionality affects http, mqtt and rtsp. three whole protocols, we love a multi-talented queen 👑

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✨ EXAMPLE ✨

extern char *large_chunk; /* pointer to somewhere */

int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    const char *data = large_chunk;
    curl_off_t length_of_data = 12345; /* set somehow */

    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");

    /* size of the POST data */
    curl_easy_setopt(curl, CURLOPT_POSTFIELDSIZE_LARGE, length_of_data);

    curl_easy_setopt(curl, CURLOPT_POSTFIELDS, data);

    curl_easy_perform(curl);
  }
}

see how we told it the size before handing it the fields? that's the whole trick bestie, the way that this works is genuinely so satisfying ⭐

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✨ AVAILABILITY ✨

Added in curl 7.11.1 — she's been around a minute, an OG fr fr 🦋

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✨ RETURN VALUE ✨

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

CURLE_OK (0) means everything was OK 😌✨ and non-zero means an error occurred — go check libcurl-errors(3) for the tea 🙈

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✨ SEE ALSO ✨

• CURLOPT_COPYPOSTFIELDS(3)
• CURLOPT_POSTFIELDS(3)
• CURLOPT_POSTFIELDSIZE(3)

like the whole POST-fields friend group, they all hang out together 💅

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and that's the page!! brought to you by libcurl, dated 2026-10-12, from the CURLOPT_POSTFIELDSIZE_LARGE(3) corner of the Library Functions Manual — go post some binary data, you absolute main character 🎀💖