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:

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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;

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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.

Yeah. That was an oopsy. Never posted in this forum before and hit return at the wrong time.

> 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.

Quote:

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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.

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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

Quote:

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Originally Posted by zacs7

> 8-bit unsigned
> 16-bit unsigned
Who says they have that many bits!?

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Microchip does, actually. I'm programming one of their microcontrollers.

Quote:

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Originally Posted by zacs7

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

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Yes, that is the definition of a union. I'm not trying to store two things at the same time. I'm simply trying to access the same data different ways.

Thanks for your input.

Quote:

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Originally Posted by matsp

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]).

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You guessed it. I want it to look like a data buffer for transmitting accross a network. I had tried typecasting in an earlier incarnation of this project on a different platform with much confusion and little success. If the net result is the same I think I prefer defining a union, if simply for my peace of mind. Obviously I still have a lot to learn; that's why I'm here

Quote:

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Originally Posted by matsp

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).

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I suspected as much.

Quote:

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Originally Posted by matsp

Of course this:

Code:

---

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

---

I probably want to write as:

Code:

---

  sReading    sensor[4];

---

?

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Yeah; I'm not sure why I ended up with that construct.

Thanks for your assistance.