Append text or data to text file in Swift -

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i have read read , write data text file

i need append data (a string) end of text file.
1 obvious way read file disk , append string end of , write back, not efficient, if dealing large files , doing in often.

so question "how append string end of text file, without reading file , writing whole thing back"?

so far have: 

    let dir:nsurl = nsfilemanager.defaultmanager().urlsfordirectory(nssearchpathdirectory.cachesdirectory, indomains: nssearchpathdomainmask.userdomainmask).last nsurl     let fileurl =  dir.urlbyappendingpathcomponent("log.txt")     var err:nserror?     // until find way append stuff files     if let current_content_of_file = nsstring(contentsofurl: fileurl, encoding: nsutf8stringencoding, error: &err) {         "\(current_content_of_file)\n\(nsdate()) -> \(object)".writetourl(fileurl, atomically: true, encoding: nsutf8stringencoding, error: &err)     }else {         "\(nsdate()) -> \(object)".writetourl(fileurl, atomically: true, encoding: nsutf8stringencoding, error: &err)     }     if err != nil{         println("cannot log: \(err)")     }

you should use nsfilehandle, can seek end of file

let dir:nsurl = nsfilemanager.defaultmanager().urlsfordirectory(nssearchpathdirectory.cachesdirectory, indomains: nssearchpathdomainmask.userdomainmask).last nsurl let fileurl =  dir.urlbyappendingpathcomponent("log.txt")  let string = "\(nsdate())\n" let data = string.datausingencoding(nsutf8stringencoding, allowlossyconversion: false)!  if nsfilemanager.defaultmanager().fileexistsatpath(fileurl.path!) {     var err:nserror?     if let filehandle = nsfilehandle(forwritingtourl: fileurl, error: &err) {         filehandle.seektoendoffile()         filehandle.writedata(data)         filehandle.closefile()     }     else {         println("can't open filehandle \(err)")     } } else {     var err:nserror?     if !data.writetourl(fileurl, options: .datawritingatomic, error: &err) {         println("can't write \(err)")     } }

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