iOS疯狂详解之NSFileHandle

//  创建一个文件
- (void)addField
{
    NSString *documentPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];

    NSString *fieldPath = [documentPath stringByAppendingPathComponent:@"student.txt"];
    
    NSLog(@"%@",fieldPath);
    
    NSString *txt = @"wanglong";
    
    [txt writeToFile:fieldPath atomically:YES encoding:NSUTF8StringEncoding error:nil];
    
    //  从路径中 读取文件 获取NSFileHandle对象
    NSFileHandle *handle = [NSFileHandle fileHandleForUpdatingAtPath:fieldPath];
    
    //  获取文件内容的 结束偏移量
    unsigned long long endOffset = handle.seekToEndOfFile;
    
    [handle seekToFileOffset:4];
    
    //  获取当前的偏移量 初始偏移量为0
    unsigned long long offset = handle.offsetInFile;
    
    //  准备要写入的字符串
    NSString *str = @"123";
    NSData *data = [str dataUsingEncoding:NSUTF8StringEncoding];
    
    [handle writeData:data];
    
    
    NSString *saveStr = [NSString stringWithContentsOfFile:fieldPath encoding:NSUTF8StringEncoding error:nil];
    
    NSLog(@"%@",saveStr);
 
//  -------------------------------------------------------
   
    
    //  覆盖数据
    NSFileHandle * srcFile, * destFile; //  输入文件、输出文件
    NSData * buffer;//  读取的缓冲数据
    NSFileManager * manager = [NSFileManager defaultManager];
    
    NSString * sourcePath = [documentPath stringByAppendingPathComponent:@"sourceFile.txt"];//  源文件路径
    
    NSLog(@"%@",sourcePath);
    
    [manager createFileAtPath:sourcePath contents:[@"Hello" dataUsingEncoding:NSUTF8StringEncoding] attributes:nil];
    
    NSString * destPath = [documentPath stringByAppendingPathComponent:@"destFile.txt"];//  输出文件路径
    BOOL success = [manager createFileAtPath:destPath contents:[@"abcdef" dataUsingEncoding:NSUTF8StringEncoding] attributes:nil];
    if (!success) {
        return;
    }
    srcFile = [NSFileHandle fileHandleForReadingAtPath:sourcePath];
    if (!destFile) {
        return;
    }
    destFile = [NSFileHandle fileHandleForWritingAtPath:destPath];
    if (!destFile) {
        return;
    }
    [destFile truncateFileAtOffset:0];//  将输出文件的长度设为0,(也就是将原来的文件清空)
    buffer = [srcFile readDataToEndOfFile];//  读取数据
    [destFile writeData:buffer];
    [srcFile closeFile];
    [destFile closeFile];
    
    
    
    
}


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