NSFileHandle(文件对接器)

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
   //由于文件对接器不能创建文件,所以必须借助文件管理器创建文件,
    NSString *documents = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES)[0];
    
    NSString *filePath = [documents stringByAppendingPathComponent:@"text.txt"];
    NSString *str = @"123456789abcdedfghij";
    [str writeToFile:filePath atomically:YES encoding:NSUTF8StringEncoding error:nil];
    NSLog(@"%@",filePath);
    
    //文件对接器,对文件内容进行操作
    
    //读取
    NSFileHandle *readFileHandle = [NSFileHandle fileHandleForReadingAtPath:filePath];
    //从文件中得到可用数据
    //NSData *availableData = [readFileHandle availableData];
    //NSLog(@"%@",[[NSString alloc] initWithData:availableData encoding:NSUTF8StringEncoding]);
    
    //从当前节点,读取指定长度的数据,须把前边的availbleData注掉,不然取不到
    NSData *lengthData = [readFileHandle readDataOfLength:10];
    NSLog(@"%@",[[NSString alloc] initWithData:lengthData encoding:NSUTF8StringEncoding]);
    
    //设置节点偏移量
    [readFileHandle seekToFileOffset:0];
    NSData *lengthData2 = [readFileHandle readDataOfLength:5];
    NSLog(@"%@",[[NSString alloc] initWithData:lengthData2 encoding:NSUTF8StringEncoding]);
    
    NSData *lengthData3 = [readFileHandle readDataOfLength:5];
    NSLog(@"%@",[[NSString alloc] initWithData:lengthData3 encoding:NSUTF8StringEncoding]);
    //从当前节点读取到文件末尾
    NSData *endData = [readFileHandle readDataToEndOfFile];
    NSLog(@"%@",[[NSString alloc] initWithData:endData encoding:NSUTF8StringEncoding]);
    
    //关闭文件
    [readFileHandle closeFile];
    //写入数据
    NSFileHandle *writeHandle = [NSFileHandle fileHandleForWritingAtPath:filePath];
    
    //设置节点位置
    [writeHandle  seekToFileOffset:10];
    //写入
    [writeHandle writeData:lengthData];
    //获取节点偏移量
    NSInteger offset = [writeHandle offsetInFile];
    NSLog(@"%ld",offset);
    
    //将文件长度设置为偏移量
    [writeHandle truncateFileAtOffset:40];
    //关闭文件
    [writeHandle closeFile];
    
    
}