CURLOPT_PROGRESSFUNCTION(3)

💖 CURLOPT_PROGRESSFUNCTION(3) 💖

okay so this is the Library Functions Manual page for CURLOPT_PROGRESSFUNCTION(3), and bestie, it’s giving “old reliable callback with a deprecated-era warning” ✨

🎀 NAME 🎀

CURLOPT_PROGRESSFUNCTION — progress meter callback 💅

✨ SYNOPSIS ✨

       #include <curl/curl.h>

       int progress_callback(void *clientp,
                             double dltotal,
                             double dlnow,
                             double ultotal,
                             double ulnow);

       CURLcode curl_easy_setopt(CURL *handle, CURLOPT_PROGRESSFUNCTION,
                                 progress_callback);

🦋 DESCRIPTION 🦋

Pass a pointer to your callback function, and make it match the prototype shown above, okay? 💖

🚨 real talk: this option is deprecated, and the curl besties encourage you to use the newer CURLOPT_XFERINFOFUNCTION(3) instead, if you can.

This function gets called by libcurl instead of its internal equivalent, at a frequent interval. While data is being transferred, it gets invoked frequently; during slow periods — like when nothing is being transferred — it can slow down to about one call per second. 🕰️

So the callback gets the tea on how much data libcurl is about to transfer and has transferred, in number of bytes:

• clientp — the pointer set with CURLOPT_PROGRESSDATA(3). libcurl does not use it; it just passes it along from the application to the callback.
• dltotal — the total number of bytes libcurl expects to download in this transfer.
• dlnow — the number of bytes downloaded so far.
• ultotal — the total number of bytes libcurl expects to upload in this transfer.
• ulnow — the number of bytes uploaded so far.

Unknown/unused argument values passed to the callback get set to zero (like if you only download data, the upload size remains 0). And many times the callback gets called one or more times first, before it knows the data sizes, so your program has to be made to handle that 😭

Return 0 from the callback if everything is fine. ✨

If your callback function returns CURL_PROGRESSFUNC_CONTINUE, it causes libcurl to continue executing the default progress function. 🔁

Return 1 from this callback to make libcurl abort the transfer and return CURLE_ABORTED_BY_CALLBACK. 💀

If you transfer data with the multi interface, this function is not called during periods of idleness unless you call the appropriate libcurl function that performs transfers. 🫶

👑 one important vibe check: CURLOPT_NOPROGRESS(3) must be set to 0 to make this function actually get called.

🌸 DEFAULT 🌸

NULL. libcurl has an internal progress meter. That is rarely wanted by users. 🙈

🌈 PROTOCOLS 🌈

This functionality affects all supported protocols ✨

🧚 EXAMPLE 🧚

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

       static int progress_callback(void *clientp,
                                    double dltotal,
                                    double dlnow,
                                    double ultotal,
                                    double ulnow)
       {
         struct progress *memory = clientp;
         printf("private: %p\n", memory->private);

         /* use the values */

         return 0; /* all is good */
       }

       int main(void)
       {
         struct progress data;

         CURL *curl = curl_easy_init();
         if(curl) {
           /* pass struct to callback  */
           curl_easy_setopt(curl, CURLOPT_PROGRESSDATA, &data);
           curl_easy_setopt(curl, CURLOPT_PROGRESSFUNCTION, progress_callback);

           curl_easy_perform(curl);
         }
       }

💀 DEPRECATED 💀

Deprecated since 7.32.0. 💅

⭐ AVAILABILITY ⭐

Added in curl 7.1 ✨

🫶 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, see libcurl-errors(3).

🔥 SEE ALSO 🔥

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

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and that’s the page, bestie 🫶 source/version: libcurl; date: 2026-10-12; page: CURLOPT_PROGRESSFUNCTION(3). byeeee ✨💅