Thread: Defining a Union - A Question of Style

Hi All,

Please excuse my profound ignorance and inevitable lack of tact. I have a simple question about defining a structure/union. Is there a more elegant, possibly simpler way to achieve the following?

Code:

typedef unsigned char       BYTE;     // 8-bit unsigned
typedef unsigned short int  WORD;     // 16-bit unsigned

typedef struct{
  BYTE month;
  BYTE day;
  BYTE hour;
  BYTE minute;
  BYTE second;
}sTimeStamp;

typedef struct{
  WORD  resolution  :4;
  WORD  temperature :12;
}sReading;
  
typedef struct{
  sTimeStamp  time;
  sReading    sensor1;
  sReading    sensor2;
  sReading    sensor3;
  sReading    sensor4;
}sSample;

typedef union{
  sSample   elements;
  BYTE      bytes[sizeof(sSample)];
}uSample;

The goal is to end up with a union allowing the same data to be referenced in different contexts - as in discrete elements or as a data buffer.
This method strikes me as a bit verbose, but fairly comprehensible.

Thanks for any input.

Next time, you might want to write your entire post out in a text editor instead of posting it halfway and then going back to edit it.

> 8-bit unsigned
> 16-bit unsigned
Who says they have that many bits!? Look at limits.h where they're defined on a case-by-case basis.

A union will mean one or the other, not both.

Originally Posted by clark.leach

The goal is to end up with a union allowing the same data to be referenced in different contexts - as in discrete elements or as a data buffer.
This method strikes me as a bit verbose, but fairly comprehensible.

One question: Why do you need it as a data buffer? For most intents and purposes, I'd expect that just casting the address of the struct to BYTE * or unsigned char * will be sufficient if you need to have it as a raw buffer (e.g. for disk writes/reads or sending across a network [beware of byte order differences in both cases]).

As far as I can see, there's nothing wrong with this method. Not sure how you could make it smaller (except for declaring all the sub-structs inside the union, but that would only save a couple of lines and make it MUCH harder to follow).

Of course this:

Code:

  sReading    sensor1;
  sReading    sensor2;
  sReading    sensor3;
  sReading    sensor4;

I probably want to write as:

Code:

  sReading    sensor[4];

?

--
Mats