day08-02-文件内容操作

Objective-c

//  main.m
//  day08-02-文件内容操作
//
//  Created by Aaron on 15/7/10.
//  Copyright (c) 2015年 Aaron. All rights reserved.
//
#import <Foundation/Foundation.h>
#if 0
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        //NSFileHandle
        //句柄
        //对句柄做操作相当于是在操作文件本身
        //读----磁盘转移到内存
        //写----内存转移到磁盘
        NSFileManager *manager = [NSFileManager defaultManager];
        [manager createFileAtPath:@"/users/Aaron/desktop/file1.txt" contents:nil attributes:nil];
        //创建文件句柄
        NSFileHandle *writeHandle = [NSFileHandle fileHandleForWritingAtPath:@"/users/Aaron/desktop/file1.txt"];
        NSString *str = @"helloworld";
        //将文件内容转成二进制数据流
        NSData *data = [str dataUsingEncoding:NSUTF8StringEncoding];
        //重新设置句柄的位置
        //注意:句柄是从0开始的
        //从第4个字符开始写入
        [writeHandle seekToFileOffset:5];
        //从文件的最后一个字符开始写入
        //[writeHandle seekToEndOfFile];
        //正式写入
        [writeHandle writeData:data];
        //同步磁盘
        [writeHandle synchronizeFile];
        //关闭文件
        [writeHandle closeFile];
    }
    return 0;
}
#endif
int main()
{
    //读文件
    NSFileHandle *readHandle = [NSFileHandle fileHandleForReadingAtPath:@"/users/qianfeng/desktop/file.txt"];
    //取出文件中4个字符（从头开始取）
    NSData *data = [readHandle readDataOfLength:4];
    NSString *str = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
    NSLog(@"%@",str);
    //从第二个字符开始取
    [readHandle seekToFileOffset:2];
    //取字符的长度是2
    data = [readHandle readDataOfLength:2];
    str = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
    NSLog(@"%@",str);
    [readHandle closeFile];
}