curl_url_set - Man Page

set a URL part


#include <curl/curl.h>

CURLUcode curl_url_set(CURLU *url,
                       CURLUPart part,
                       const char *content,
                       unsigned int flags)


Given the url handle of an already parsed URL, this function lets the user set/update individual pieces of it.

The part argument should identify the particular URL part (see list below) to set or change, with content pointing to a null-terminated string with the new contents for that URL part. The contents should be in the form and encoding they'd use in a URL: URL encoded.

The application does not have to keep content around after a successful call.

Setting a part to a NULL pointer will effectively remove that part's contents from the CURLU handle.

By default, this API only accepts URLs using schemes for protocols that are supported built-in. To make libcurl parse URLs generically even for schemes it does not know about, the CURLU_NON_SUPPORT_SCHEME flags bit must be set. Otherwise, this function returns CURLUE_UNSUPPORTED_SCHEME on URL schemes it does not recognize.

This function call has no particular maximum length for any provided input string. In the real world, excessively long field in URLs will cause problems even if this API accepts them.

When setting or updating contents of individual URL parts, this API might accept data that would not be otherwise possible to set in the string when it gets populated as a result of a full URL parse. Beware. If done so, extracting a full URL later on from such components might render an invalid URL.

The flags argument is a bitmask with independent features.



Allows the full URL of the handle to be replaced. If the handle already is populated with a URL, the new URL can be relative to the previous.

When successfully setting a new URL, relative or absolute, the handle contents will be replaced with the information of the newly set URL.

Pass a pointer to a null-terminated string to the url parameter. The string must point to a correctly formatted "RFC 3986+" URL or be a NULL pointer.

Unless CURLU_NO_AUTHORITY is set, a blank host name is not allowed in the URL.


Scheme cannot be URL decoded on set. libcurl only accepts setting schemes up to 40 bytes long.


The options field is an optional field that might follow the password in the userinfo part. It is only recognized/used when parsing URLs for the following schemes: pop3, smtp and imap. This function however allows users to independently set this field at will.


The host name. If it is IDNA the string must then be encoded as your locale says or UTF-8 (when WinIDN is used). If it is a bracketed IPv6 numeric address it may contain a zone id (or you can use CURLUPART_ZONEID).

Unless CURLU_NO_AUTHORITY is set, a blank host name is not allowed to set.


If the host name is a numeric IPv6 address, this field can also be set.


Port cannot be URL encoded on set. The given port number is provided as a string and the decimal number must be between 1 and 65535. Anything else will return an error.


If a path is set in the URL without a leading slash, a slash will be inserted automatically when this URL is read from the handle.


The query part will also get spaces converted to pluses when asked to URL encode on set with the CURLU_URLENCODE bit.

If used together with the CURLU_APPENDQUERY bit, the provided part is appended on the end of the existing query.

The question mark in the URL is not part of the actual query contents.


The hash sign in the URL is not part of the actual fragment contents.


The flags argument is zero, one or more bits set in a bitmask.


Can be used when setting the CURLUPART_QUERY component. The provided new part will then instead be appended at the end of the existing query - and if the previous part did not end with an ampersand (&), an ampersand gets inserted before the new appended part.

When CURLU_APPENDQUERY is used together with CURLU_URLENCODE, the first '=' symbol will not be URL encoded.


If set, allows curl_url_set(3) to set a non-supported scheme.


When set, curl_url_set(3) URL encodes the part on entry, except for scheme, port and URL.

When setting the path component with URL encoding enabled, the slash character will be skipped.

The query part gets space-to-plus conversion before the URL conversion.

This URL encoding is charset unaware and will convert the input on a byte-by-byte manner.


If set, will make libcurl allow the URL to be set without a scheme and then sets that to the default scheme: HTTPS. Overrides the CURLU_GUESS_SCHEME option if both are set.


If set, will make libcurl allow the URL to be set without a scheme and it instead "guesses" which scheme that was intended based on the host name. If the outermost sub-domain name matches DICT, FTP, IMAP, LDAP, POP3 or SMTP then that scheme will be used, otherwise it picks HTTP. Conflicts with the CURLU_DEFAULT_SCHEME option which takes precedence if both are set.


If set, skips authority checks. The RFC allows individual schemes to omit the host part (normally the only mandatory part of the authority), but libcurl cannot know whether this is permitted for custom schemes. Specifying the flag permits empty authority sections, similar to how file scheme is handled.


When set for CURLUPART_URL, this makes libcurl skip the normalization of the path. That is the procedure where curl otherwise removes sequences of dot-slash and dot-dot etc. The same option used for transfers is called CURLOPT_PATH_AS_IS(3).


If set, the URL parser allows space (ASCII 32) where possible. The URL syntax does normally not allow spaces anywhere, but they should be encoded as %20 or '+'. When spaces are allowed, they are still not allowed in the scheme. When space is used and allowed in a URL, it will be stored as-is unless CURLU_URLENCODE is also set, which then makes libcurl URL-encode the space before stored. This affects how the URL will be constructed when curl_url_get(3) is subsequently used to extract the full URL or individual parts. (Added in 7.78.0)


If set, the URL parser will not accept embedded credentials for the CURLUPART_URL, and will instead return CURLUE_USER_NOT_ALLOWED for such URLs.


  CURLUcode rc;
  CURLU *url = curl_url();
  rc = curl_url_set(url, CURLUPART_URL, "", 0);
  if(!rc) {
    char *scheme;
    /* change it to an FTP URL */
    rc = curl_url_set(url, CURLUPART_SCHEME, "ftp", 0);


Added in 7.62.0. CURLUPART_ZONEID was added in 7.65.0.

Return Value

Returns a CURLUcode error value, which is CURLUE_OK (0) if everything went fine. See the libcurl-errors(3) man page for the full list with descriptions.

A URL string passed on to curl_url_set(3) for the CURLUPART_URL part, must be shorter than 8000000 bytes otherwise it returns CURLUE_MALFORMED_INPUT (added in 7.65.0).

If this function returns an error, no URL part is set.

See Also

curl_url_cleanup(3), curl_url(3), curl_url_get(3), curl_url_dup(3), curl_url_strerror(3), CURLOPT_CURLU(3)

Referenced By

CURLOPT_CURLU(3), curl_url(3), curl_url_cleanup(3), curl_url_dup(3), curl_url_get(3), curl_url_strerror(3), libcurl-url(3).

April 26, 2023 libcurl 8.1.1