iPhone写入二进制数据 [英] iPhone writing binary data

问题描述

你怎么写二进制数据到一个文件？我想写花车到一个文件中，原，然后读取回为浮动。你是怎么做到的？

How do you write binary data to a file? I want to write floats to a file, raw, and then read them back as floats. How do you do that?

推荐答案

被这个实验：

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); 
NSString *documentsDirectory = [paths objectAtIndex:0];

NSString *file = [documentsDirectory stringByAppendingPathComponent:@"binaryData"];

float b = 32.0f;

NSMutableData *data = [NSMutableData dataWithLength:sizeof(float)];
[data appendBytes:&b length:sizeof(float)];
[data writeToFile:file atomically:YES];

NSData *read = [NSData dataWithContentsOfFile:file];
float b2;
NSRange test = {0,4};
[read getBytes:&b2 range:test];

奇怪的是，写入的文件似乎是8个字节，而不是4甚至可以用0长度初始化NSData的，追加一个浮动，然后写，然后该文件将4个字节。为什么NSData的默认添加4个字节？长度为4 NSData的一应导致文件长度为4，而不是8。

The weird thing is that the file written seems to be 8 bytes and not 4. It is even possible to init the nsdata with 0 length, append a float and then write, and then the file will be 4 bytes. Why is NSData adding 4 bytes by default? A NSData with length 4 should result in a file with length 4, not 8.

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