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Assert unique values for a struct member during compile.

Posted on 2014-03-01
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Last Modified: 2014-03-03
I have an embedded application where I need to guarantee that a structure member has a unique value in a table of those structures. I need to ensure that the startingPosition is always unique.

const dataLogDefinition dataLogDefinitions PPAGE_E5 = {
		version:  PROTOCOL_VERSION,
		sizeOfEntry:  sizeof(dataLogField),
		entries: {
				 {.startingPosition = offsetof(CoreVar, IAT), .size = bitSize(CoreVar, IAT), .name = "IAT", .description = "Variable 1", 0,0},
				 {.startingPosition = offsetof(CoreVar, CHT), .size = bitSize(CoreVar, CHT), .name = "CHT", .description = "Variable 2", 0,0},
		}
};

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Any ideas would be appreciated.
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Question by:sean-keys
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6 Comments
 
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Expert Comment

by:Kdo
ID: 39897547
Hi Sean,

Is the table static?  How many items are in the table?  Is uniqueness enough or do they also need to be sequential, non-descending, random, etc.
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Author Comment

by:sean-keys
ID: 39897563
Hi,

Yes the table is static. The length will be variable but within reason 20-30 entries. They do not need to be sequential, I just need to make sure something does not end up in there twice.
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Author Comment

by:sean-keys
ID: 39897577
https://git.libreems.org/libreems-suite/libreems-firmware/blob/dataLogDefProtocol/src/main/dataLogDefinitions.c

needs to describe the data here:

https://git.libreems.org/libreems-suite/libreems-firmware/blob/dataLogDefProtocol/src/main/inc/containerTypes.h#L72


The definitions need to remain seperate because they reside in flash while the other resides in RAM, which I have much less of.

Thanks!
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LVL 45

Accepted Solution

by:
Kdo earned 500 total points
ID: 39897697
Easy enough.  :)

Note the two sample lines:

                         {.startingPosition = offsetof(CoreVar, IAT), .size = bitSize(CoreVar, IAT), .name = "IAT", .description = "Variable 1", 0,0},
                         {.startingPosition = offsetof(CoreVar, CHT), .size = bitSize(CoreVar, CHT), .name = "CHT", .description = "Variable 2", 0,0},

The first line contains the string "IAT" and the constant IAT.  IAT is defined in the header file.
The second line has the same characteristics, except that the values are "CHT" and CHT.

I suggest that you simply enumerate the items that you need.


enum
{
  SP_NULL=0,      // zero
  SP_IAT,
  SP_CHT,
  SP_TPS,
  SP_EGO,
  SP_MAP,
  SP_AAP,
  SP_BRV,
  SP_MAT,
  SP_MAX
};
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Author Closing Comment

by:sean-keys
ID: 39900630
I guess the "right" way to do this would be to have a script generate both C source files. It seems enum, is as good as it gets :)
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LVL 45

Expert Comment

by:Kdo
ID: 39900646
Well, for the specific application that you've shown, I don't think that a random/unique value is sufficient.  I believe that the value is also an index into the array of values returned from the PIC controller.  

You'll want to initialize the value to the correct index value.
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