---
name: "curl_multi_waitfds"
section: "3"
platform: "linux"
package: "curl"
version: "8.23.0-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/curl_multi_waitfds"
---

# curl\_multi\_waitfds(3)

extract file descriptor information from a multi handle

## NAME

curl\_multi\_waitfds - extract file descriptor information from a multi handle

## SYNOPSIS

```
#include <curl/curl.h>
#include <stdlib.h>
CURLMcode curl_multi_waitfds(CURLM *multi,
                             struct curl_waitfd *ufds,
                             unsigned int size,
                             unsigned int *fd_count);
```

## DESCRIPTION

This function extracts *curl\_waitfd* structures which are similar to *[poll(2)](/poll/2.md)*'s *pollfd* structure from a given multi\_handle.

These structures can be used for polling on multi\_handle file descriptors in a fashion similar to *[curl\_multi\_poll(3)](/curl_multi_poll/3.md)*. The *[curl\_multi\_perform(3)](/curl_multi_perform/3.md)* function should be called as soon as one of them is ready to be read from or written to.

libcurl fills provided *ufds* array up to the *size*. If a number of descriptors used by the multi\_handle is greater than the *size* parameter then libcurl returns CURLM\_OUT\_OF\_MEMORY error.

If the *fd\_count* argument is not a null pointer, it points to a variable that on return specifies the number of descriptors used by the multi\_handle to be checked for being ready to read or write.

The client code can pass *size* equal to zero to get the number of the descriptors and allocate appropriate storage for them to be used in a subsequent function call. In this case, *fd\_count* receives a number greater than or equal to the number of descriptors.

## PROTOCOLS

This functionality affects all supported protocols

## EXAMPLE

```
#include <stdlib.h>
int main(void)
{
  CURLMcode mresult;
  struct curl_waitfd *ufds;
  CURLM *multi = curl_multi_init();
  do {
    /* call curl_multi_perform() */
    /* get the count of file descriptors from the transfers */
    unsigned int fd_count = 0;
    mresult = curl_multi_waitfds(multi, NULL, 0, &fd_count);
    if(mresult != CURLM_OK) {
      fprintf(stderr, "curl_multi_waitfds() failed, code %d.\n", mresult);
      break;
    }
    if(!fd_count)
      continue; /* no descriptors yet */
    /* allocate storage for our descriptors */
    ufds = malloc(fd_count * sizeof(struct curl_waitfd));
    /* get wait descriptors from the transfers and put them into array. */
    mresult = curl_multi_waitfds(multi, ufds, fd_count, &fd_count);
    if(mresult != CURLM_OK) {
      fprintf(stderr, "curl_multi_waitfds() failed, code %d.\n", mresult);
      free(ufds);
      break;
    }
    /* Do polling on descriptors in ufds */
    free(ufds);
  } while(!mresult);
}
```

## AVAILABILITY

Added in curl 8.8.0

## RETURN VALUE

This function returns a CURLMcode indicating success or error.

CURLM\_OK (0) means everything was OK, non-zero means an error occurred, see *[libcurl-errors(3)](/libcurl-errors/3.md)*.

## SEE ALSO

[**curl\_multi\_fdset**(3)](/curl_multi_fdset/3.md), [**curl\_multi\_perform**(3)](/curl_multi_perform/3.md), [**curl\_multi\_poll**(3)](/curl_multi_poll/3.md), [**curl\_multi\_wait**(3)](/curl_multi_wait/3.md)