CURLOPT_PROGRESSFUNCTION(3) Library Functions ManualCURLOPT_PROGRESSFUNCTION(3)
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, which should match the proto-
type shown above.
This option is deprecated and we encourage users to use the newer CUR-
LOPT_XFERINFOFUNCTION(3) instead, if you can.
This function gets called by libcurl instead of its internal equivalent
with a frequent interval. While data is being transferred it is invoked
frequently, and during slow periods like when nothing is being trans-
ferred it can slow down to about one call per second.
clientp is the pointer set with CURLOPT_PROGRESSDATA(3), it is not used
by libcurl but is only passed along from the application to the call-
back.
The callback gets told how much data libcurl is about to transfer and
has transferred, in number of bytes. dltotal is the total number of
bytes libcurl expects to download in this transfer. dlnow is the number
of bytes downloaded so far. ultotal is the total number of bytes libcurl
expects to upload in this transfer. ulnow is the number of bytes up-
loaded so far.
Unknown/unused argument values passed to the callback are be set to zero
(like if you only download data, the upload size remains 0). Many times
the callback is called one or more times first, before it knows the data
sizes so a program must be made to handle that.
Return zero 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 re-
turn 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.
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)
libcurl 2026-07-12 CURLOPT_PROGRESSFUNCTION(3)
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