NSFileHandler---初步理解

来源：互联网发布：编程过滤器的工作原理编辑：程序博客网时间：2024/06/06 03:04
     NSString *docPath = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES)[0];        NSString *filePath = [docPath stringByAppendingString:@"/1.txt"];        NSString *str = @"My name is Leon, Hello everyone";        [str writeToFile:filePath atomically:YES encoding:NSUTF8StringEncoding error:nil];                NSString *readstr = [[NSString alloc] initWithContentsOfFile:filePath encoding:NSUTF8StringEncoding error:nil];        NSLog(@"readstr:%@", readstr);                // 输出        NSFileHandle *output = [NSFileHandle fileHandleForReadingAtPath:filePath];        // 读取availableData        NSData *data = output.availableData;        // 读取的长度 data.length        //        NSString *availableDataStr = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];        //        // readDataToEndOfFile 这个方法你先要定义好当前节点  否则读不到东西        [output seekToFileOffset:0];        NSData *readtoendData = [output readDataToEndOfFile];        NSString *readToEndStr = [[NSString alloc] initWithData:readtoendData encoding:NSUTF8StringEncoding];                // readDataOfLength从当前节点开始读取指定的长度数        // 这个方法你先要定义好当前节点否则读不到东西 要重新定义当前节点          [output seekToFileOffset:0];        NSData *readDataOfLengthData = [output readDataOfLength:2];        NSString *readDataOfLengthStr = [[NSString alloc] initWithData:readDataOfLengthData encoding:NSUTF8StringEncoding];         NSLog(@"availableDataStr:%@, readToEndStr:%@， readDataOfLengthStr:%@", availableDataStr, readToEndStr, readDataOfLengthStr);        // 关闭输出        [output closeFile];                        // 输入        NSFileHandle *input = [NSFileHandle fileHandleForWritingAtPath:filePath];        // 读取当时的偏移量        unsigned long long offset = [input offsetInFile];        NSLog(@"%llu", offset);                 // 跳转        [input seekToFileOffset:2];        unsigned long long newoffset = [input offsetInFile];        NSLog(@"%llu", newoffset);                // 跳转到末尾        [input seekToEndOfFile];         newoffset = [input offsetInFile];        NSLog(@"%llu", newoffset);        // 往文件末尾插入字符        NSString *addStr = @"Hi, I am Mike";        NSData *addData = [addStr dataUsingEncoding:NSUTF8StringEncoding];        [input seekToEndOfFile];        [input writeData:addData];        // 不知道有什么用//        [input truncateFileAtOffset:0];        [input closeFile];                NSString *newStr = [[NSString alloc] initWithContentsOfFile:filePath encoding:NSUTF8StringEncoding error:nil];        NSLog(@"newStr:%@", newStr);
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