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Using constants in ternaries

 
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coder
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Using constants in ternaries
PostPosted: Fri Oct 03, 2008 6:31 pm     Reply with quote
Hey,

I'm trying to get the following code to compile.

Code:

   char c;
   int bool = 1;
   const int constBool = 1;
   const char constArray[1] = {'a'};
   char array[1] = {'a'};

   c = (bool ? constArray : constArray)[0];


While trying to fix this problem, I noticed that the following code compiles. The variables are declared the same as above.

Code:

   c = (bool ? constArray : array)[0];
   c = (constBool ? constArray : constArray)[0];


I could move my arrays into RAM instead of ROM by not declaring them constant, but the arrays I'm working with are large, so I'd rather put them in ROM if possible. I'm also curious as to why this is occurring. Any help would be appreciated.

Thanks
FvM



Joined: 27 Aug 2008
Posts: 2337
Location: Germany

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PostPosted: Sat Oct 04, 2008 1:57 am     Reply with quote
Hello,

ROM arrays imply a special handling of the data, where a call to a read function is inserted in the code for each assignment. Pointers to an ROM array are not provided by CCS C in default CONST mode.

Your construct
Code:
c = (bool ? constArray : constArray)[0];

implies calculating a pointer, that is dereferenced afterwards. This doesn't work with ROM constants.

Regards,
Frank

P.S.

A construct using strings directly rather than pointers should work:
Code:
   c = (bool ? constArray[0] : constArray[0]);
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