# CFNetServiceBrowserSearchForDomains(_:_:_:) Searches for domains. ``` func CFNetServiceBrowserSearchForDomains(_ browser: CFNetServiceBrowser, _ registrationDomains: Bool, _ error: UnsafeMutablePointer?) -> Bool ``` ## Parameters `browser` The CFNetServiceBrowser, obtained by previously calling [`CFNetServiceBrowserCreate(_:_:_:)`](/documentation/CFNetwork/CFNetServiceBrowserCreate(_:_:_:)), that is to perform the search; cannot be `NULL`. `registrationDomains` `TRUE` to search for only registration domains; `FALSE` to search for domains that can be browsed for services. For this version of the CFNetServices API, the registration domain is the local domain maintained by the mDNS responder running on the same machine as the calling application. `error` A pointer to a structure, that, if an error occurs, will be set to the error and the error’s domain and passed to your callback function. Pass `NULL` if you don’t want to receive the error that may occur as a result of this particular call. ## Return Value `TRUE` if the search was started (asynchronous mode); `FALSE` if another search is already in progress for this CFNetServiceBrowser or if an error occurred. ## Discussion This function uses a CFNetServiceBrowser to search for domains. The search continues until the search is canceled by calling [`CFNetServiceBrowserStopSearch(_:_:)`](/documentation/CFNetwork/CFNetServiceBrowserStopSearch(_:_:)). If `registrationDomains` is `TRUE`, this function searches only for domains in which services can be registered. If `registrationDomains` is `FALSE`, this function searches for domains that can be browsed for services. When a domain is found, the callback function specified when the CFNetServiceBrowser was created is called and passed an instance of a CFStringRef containing the domain that was found. In asynchronous mode, this function returns `TRUE` if the search was started. Otherwise, it returns `FALSE`. In synchronous mode, this function blocks until the search is stopped by calling [`CFNetServiceBrowserStopSearch(_:_:)`](/documentation/CFNetwork/CFNetServiceBrowserStopSearch(_:_:)) from another thread, in which case it returns `FALSE`, or until an error occurs. ### Special Considerations This function is thread safe. For any one CFNetServiceBrowser, only one domain search or one service search can be in progress at the same time. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)