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curl_url_set(3) libcurl Manual curl_url_set(3)


curl_url_set - 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.

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

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.

Scheme cannot be URL decoded on set.
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).
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 will be appended on the end of the existing query - and if the previous part didn't end with an ampersand (&), an ampersand will be inserted before the new appended part.

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

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.

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.


Returns a CURLUcode error value, which is CURLUE_OK (0) if everything went fine.

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.


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 curl 7.62.0. CURLUPART_ZONEID was added in 7.65.0.


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

November 4, 2020 libcurl 7.74.0