[Objective-C] Introduction to NSFileHandle in OC and common usage

NSFileHandle NSFileManager class is mainly used for file operations (such as deleting, modifying, moving, and assigning values) The NSFileHandle class mainly reads and writes the file content. NSFileHandle 1: Create an NSFileHandle object 2: perform I/O operations on open files 3. Disable object operations. Common Handling Methods   + (Id) fileHandleForReadingAtPath :( NSString *) path; // open a file to prepare for reading + (id) fileHandleForWritingAtPath :( NSString *) path; // open a file to prepare for writing + (id) fileHandleForUpdatingAtPath :( NSString *) path; // open a file and update (read, write)-(NSData *) availableData; // return available data-(NSData *) readDataToEndOfFile; // read data from the current node location to the end of the file-(NSData *) readDataOfLength :( NSUInteger) length; // read data of the specified length from the current node location-(void) writeData :( NSData *) data; // write data-(unsigned long) offsetInFile; // obtain the offset of the current file-(unsigned long) seekToEndOfFile; // jump to the end of the file-(void) seekToFileOffset :( unsigned long) offset; // jump to the specified offset position of the specified file-(void) truncateFileAtOffset :( unsigned long) offset; // set the file length-(void) synchronizeFile; // file synchronization-(void) closeFile; // close the file   Instance code 1 (add data to the file :): @ Autoreleasepool { NSString * homePath = NSHomeDirectory (); NSLog (@ "% @", homePath); NSString * filePath = [homePath stringByAppendingFormat: @ "/Desktop/testfile"]; NSLog (@ "% @", filePath); NSFileHandle * fileHandle = [NSFileHandle fileHandleForUpdatingAtPath: filePath]; [fileHandle seekToEndOfFile]; NSString * str = @ "The data added to the test is "; NSData * data = [str dataUsingEncoding: NSUTF8StringEncoding]; [fileHandle writeData: data]; [fileHandle closeFile];} return 0;     2: locate the data in the file:   NSString *homePath=NSHomeDirectory(); NSString *filePath=[homePath stringByAppendingFormat:@"/Desktop/testfile"]; NSFileHandle *fileHandle=[NSFileHandle fileHandleForReadingAtPath:filePath]; NSUInteger length= [fileHandle availableData].length; [fileHandle seekToFileOffset:length/2]; NSData *data=[fileHandle readDataToEndOfFile]; NSString *str=[[NSString alloc]initWithData:data encoding:NSUTF8StringEncoding]; NSLog(@"%@",str); [Here are some methods of the NSData class] 3: copy the data in the file // Copy the NSString * homePath = NSHomeDirectory (); NSString * filePath = [homePath stringByAppendingFormat: @ "/Desktop/testfile"]; // NSFileHandle * fileHandle = [NSFileHandle handle: filePath]; NSString * targetPath = [homePath stringByAppendingFormat: @ "/Desktop/outfile"]; NSFileManager * fileManager = [NSFileManager defaultManager]; BOOL result = [fileManager createFileAtPath: targetPath contents: nil Attributes: nil]; if (result) {NSLog (@ "create success! ");} NSFileHandle * inFileHandle = [NSFileHandle fileHandleForReadingAtPath: filePath]; NSFileHandle * outFileHandle = [NSFileHandle handle: targetPath]; NSData * inData = [inFileHandle availableData] // read all the data in the file. // write the file [outFileHandle writeData: inData]; [inFileHandle closeFile]; [outFileHandle closeFile];