CURLOPT_DEFAULT_PROTOCOL - default protocol to use if the URL is missing a scheme name

Added in curl 7.45.0

NULL (make a guess based on the host)

This option tells libcurl to use protocol if the URL is missing a scheme name. Use one of these protocol (scheme) names: dict, file, ftp, ftps, gopher, http, https, imap, imaps, ldap, ldaps, pop3, pop3s, rtsp, scp, sftp, smb, smbs, smtp, smtps, telnet, tftp An unknown or unsupported protocol causes error CURLE_UNSUPPORTED_PROTOCOL when libcurl parses a URL without a scheme. Parsing happens when curl_easy_perform(3) or curl_multi_perform(3) is called. The protocol set supported by libcurl vary depending on how it was built. Use curl_version_info(3) if you need a list of protocol names supported by the build of libcurl that you are using. This option does not change the default proxy protocol (http). Without this option libcurl would make a guess based on the host, see CURLOPT_URL(3) for details. The application does not have to keep the string around after setting this option. Using this option multiple times makes the last set string override the previous ones. Set it to NULL to disable its use again.

int main(void) { CURL *curl = curl_easy_init(); if(curl) { /* set a URL without a scheme */ curl_easy_setopt(curl, CURLOPT_URL, "example.com"); /* set the default protocol (scheme) for schemeless URLs */ curl_easy_setopt(curl, CURLOPT_DEFAULT_PROTOCOL, "https"); /* Perform the request */ curl_easy_perform(curl); } }

CURLOPT_DEFAULT_PROTOCOL - default protocol to use if the URL is missing a scheme name

This functionality affects all supported protocols

CURLE_OK if the option is supported. CURLE_OUT_OF_MEMORY if there was insufficient heap space. CURLE_UNKNOWN_OPTION if the option is not supported.

CURLINFO_PROTOCOL(3), CURLINFO_SCHEME(3), CURLOPT_URL(3) libcurl 2025-06-16 CURLOPT_DEFAULT_PROTOCOL(3)

#include <curl/curl.h> CURLcode curl_easy_setopt(CURL *handle, CURLOPT_DEFAULT_PROTOCOL, char *protocol);