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There's any way to check the size of a define?

 
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E_Blue



Joined: 13 Apr 2011
Posts: 208

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There's any way to check the size of a define?
PostPosted: Tue Feb 20, 2018 6:31 am     Reply with quote

I have a header file that have some default values and I want to avoid the compilation if one of them is too big in length.

I tried the following code without success

Code:
#define DefaultCode "7777"

#if sizeof(DefaultCode) >4
#error "DefaultCode too big, CHECK CONFIGURATION FILE"
#endif

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Electric Blue
Ttelmah



Joined: 11 Mar 2010
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PostPosted: Tue Feb 20, 2018 8:00 am     Reply with quote

A define, does not exist.
It has no size, till you put it into a variable. The variable then has a size.

#DEFINES in C, are text macro substitutions, not variables.

All the #functions are carried out by the pre-processor, before any 'C' even exists. sizeof, is a C function, which hasn't even been loaded yet...
temtronic



Joined: 01 Jul 2010
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PostPosted: Tue Feb 20, 2018 8:31 am     Reply with quote

hmm... rainy day here..
I tired this..
...
#define BUFFER_SIZE 17
#if BUFFER_SIZE>16
#error Buffer size is too large
#endif
...

does work, well it compiles and if BUFFER_SIZE is <17 no msg appears.
when it's >16 the error msg appears

if you change
#define DefaultCode "7777"
to
#define DefaultCode 7777

then
#if DefaultCode >7777
#error Check config file
#endif

maybe it'll work ??

If you want to check for DefaultCode being more than 4 space wide, then test for >9999.

like I said rainy day here..slipping on water on ice is NOT fun.

Jay
Ttelmah



Joined: 11 Mar 2010
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PostPosted: Tue Feb 20, 2018 8:59 am     Reply with quote

Yes. The preprocessor supports arithmetic tests. But that is all.
You can test a numeric value, or it the define itself exists.
No 'strings' or sizes.

So if you made your value a numeric value as opposed to a string, you could refuse it if it was >9999. However it couldn't then contain text like "ABCD".
E_Blue



Joined: 13 Apr 2011
Posts: 208

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PostPosted: Wed Feb 28, 2018 7:47 am     Reply with quote

Thanks for your answers.
So I can apply this only to numeric values but not strings.

I guess i will must have care about those strings one by one by my self.
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Electric Blue
Ttelmah



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Posts: 13758

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PostPosted: Wed Feb 28, 2018 8:03 am     Reply with quote

In C itself, once you put the define into a variable, you can of course check this.
Code:

#define FRED "A Value"

    char var[]=FRED;
    if (strlen(var)>4)
    {


    }

But this is at run time, not compile time.

It is worth pointing out that 'sizeof' wouldn't work anyway. The sizeof a string is the size of the pointer that addresses it....
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