---
name: "CURLOPT_PRE_PROXY"
section: "3"
platform: "macos"
package: "curl"
version: "166.0.0.0.1"
release: "macOS 26.5"
platforms: ["linux", "macos"]
url: "https://new.carta.tech/CURLOPT_PRE_PROXY"
---

# CURLOPT\_PRE\_PROXY(3)

pre-proxy host to use

## NAME

CURLOPT\_PRE\_PROXY - pre-proxy host to use

## SYNOPSIS

```
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_PRE_PROXY, char *preproxy);
```

## DESCRIPTION

Set the *preproxy* to use for the upcoming request. The parameter should be a char \* to a null-terminated string holding the hostname or dotted numerical IP address. A numerical IPv6 address must be written within \[brackets\].

To specify port number in this string, append :\[port\] to the end of the host name. The proxy's port number may optionally be specified with the separate option *[CURLOPT\_PROXYPORT(3)](/CURLOPT_PROXYPORT/3.md)*. If not specified, libcurl defaults to using port 1080 for proxies.

A pre proxy is a SOCKS proxy that curl connects to before it connects to the HTTP(S) proxy specified in the *[CURLOPT\_PROXY(3)](/CURLOPT_PROXY/3.md)* option. The pre proxy can only be a SOCKS proxy.

The pre proxy string should be prefixed with \[scheme\]:// to specify which kind of socks is used. Use socks4://, socks4a://, socks5:// or socks5h:// (the last one to enable socks5 and asking the proxy to do the resolving, also known as *CURLPROXY\_SOCKS5\_HOSTNAME* type) to request the specific SOCKS version to be used. Otherwise SOCKS4 is used as default.

Setting the pre proxy string to "" (an empty string) explicitly disables the use of a pre proxy.

The application does not have to keep the string around after setting this option.

## DEFAULT

Default is NULL, meaning no pre proxy is used.

When you set a hostname to use, do not assume that there is any particular single port number used widely for proxies. Specify it!

## PROTOCOLS

All except file://. Note that some protocols do not work well over proxy.

## EXAMPLE

```
int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/file.txt");
    curl_easy_setopt(curl, CURLOPT_PRE_PROXY, "socks4://socks-proxy:1080");
    curl_easy_setopt(curl, CURLOPT_PROXY, "http://proxy:80");
    curl_easy_perform(curl);
  }
}
```

## AVAILABILITY

Added in 7.52.0

## RETURN VALUE

Returns CURLE\_OK if proxies are supported, CURLE\_UNKNOWN\_OPTION if not, or CURLE\_OUT\_OF\_MEMORY if there was insufficient heap space.

## SEE ALSO

[**CURLOPT\_HTTPPROXYTUNNEL**(3)](/CURLOPT_HTTPPROXYTUNNEL/3.md), [**CURLOPT\_PROXY**(3)](/CURLOPT_PROXY/3.md)