如何将24位整数转换为3字节数组? [英] How do I convert a 24-bit integer into a 3-byte array?

问题描述

嘿，我完全超出了我的深度，我的大脑开始受伤..:(

Hey Im totally out of my depth and my brain is starting to hurt.. :(

我需要隐藏一个整数，以使其适合3字节数组(是24位整数吗?)，然后再次返回以通过套接字从字节流中发送/接收此数字

I need to covert an integer so that it will fit in a 3 byte array.(is that a 24bit int?) and then back again to send/receive this number from a byte stream through a socket

我有:

NSMutableData* data = [NSMutableData data];

 int msg = 125;

 const void *bytes[3];

 bytes[0] = msg;
 bytes[1] = msg >> 8;
 bytes[2] = msg >> 16;

 [data appendBytes:bytes length:3];

 NSLog(@"rtn: %d", [[[NSString alloc] initWithData:data encoding:NSASCIIStringEncoding] intValue]);

 //log brings back 0

我想我的主要问题是我不知道如何检查我是否确实正确转换了int，这是我发送数据也需要做的转换.

I guess my main problem is that I do not know how to check that I have indeed converted my int correctly which is the converting back that I need to do as well for sending the data.

任何帮助都将不胜感激！

Any help greatly appreciated!

推荐答案

您可以使用联合:

union convert {
    int i;
    unsigned char c[3];
};

从int转换为字节:

union convert cvt;
cvt.i = ...
// now you can use cvt.c[0], cvt.c[1] & cvt.c[2]

从字节转换为int:

union convert cvt;
cvt.i = 0; // to clear the high byte
cvt.c[0] = ...
cvt.c[1] = ...
cvt.c[2] = ...
// now you can use cvt.i

注意:以这种方式使用联合依赖于处理器字节顺序.我给的示例将在小端系统(如x86)上工作.

Note: using unions in this manner relies on processor byte-order. The example I gave will work on a little-endian system (like x86).

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