CURLOPT\_PREREQDATA(3) Library Functions Manual CURLOPT\_PREREQDATA(3)

# [NAME](#NAME)

CURLOPT\_PREREQDATA - pointer passed to the pre-request callback

# [SYNOPSIS](#SYNOPSIS)

```
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_PREREQDATA, void *pointer);
```

# [DESCRIPTION](#DESCRIPTION)

Pass a *pointer* that is untouched by libcurl and passed as the first argument in the pre-request callback set with [*CURLOPT\_PREREQFUNCTION(3)*](/man/os/curl/CURLOPT_PREREQFUNCTION.3).

# [DEFAULT](#DEFAULT)

NULL

# [PROTOCOLS](#PROTOCOLS)

This functionality affects all supported protocols

# [EXAMPLE](#EXAMPLE)

```
struct priv {


  void *custom;
};
static int prereq_callback(void *clientp,


                           char *conn_primary_ip,


                           char *conn_local_ip,


                           int conn_primary_port,


                           int conn_local_port)
{


  printf("Connection made to %s:%d\n", conn_primary_ip, conn_primary_port);


  return CURL_PREREQFUNC_OK;
}
int main(void)
{


  struct priv prereq_data;


  CURL *curl = curl_easy_init();


  if(curl) {


    CURLcode result;


    curl_easy_setopt(curl, CURLOPT_PREREQFUNCTION, prereq_callback);


    curl_easy_setopt(curl, CURLOPT_PREREQDATA, &prereq_data);


    result = curl_easy_perform(curl);


    curl_easy_cleanup(curl);


  }
}
```

# [AVAILABILITY](#AVAILABILITY)

Added in curl 7.80.0

# [RETURN VALUE](#RETURN_VALUE)

[*curl\_easy\_setopt(3)*](/man/os/curl/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)*](/man/os/curl/libcurl-errors.3).

# [SEE ALSO](#SEE_ALSO)

[**CURLINFO\_PRIMARY\_IP**(3)](/man/os/curl/CURLINFO_PRIMARY_IP.3), [**CURLINFO\_PRIMARY\_PORT**(3)](/man/os/curl/CURLINFO_PRIMARY_PORT.3), [**CURLOPT\_PREREQFUNCTION**(3)](/man/os/curl/CURLOPT_PREREQFUNCTION.3)

2026-10-01 libcurl

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Document: CURLOPT_PREREQDATA(3) from curl 8.22.0-r4 (Chainguard OS)
Source: https://github.com/curl/curl.git