how to override #define in arduino library header

Question

I am using RunningMedian Arduino library in a project.

In the library header file the MEDIAN_MAX_SIZE is preset to 19.

     #define MEDIAN_MAX_SIZE     19  // adjust if needed

I need to override the header to make MEDIAN_MAX_SIZE 30 without changing the library files so updates can still be done in the future.

My declatations:

     #define RunningMedian::MEDIAN_MAX_SIZE 30     // library over ride ??
     #define ACTIVE_MAX 30 // max active buffer size
     RunningMedian ActiveSamples( ACTIVE_MAX ); // FIFO readings

     This will not compile.

The library code will not create a buffer greater than MEDIAN_MAX_SIZE.

How can I override the 19 for 30 without changing the RunningMedian.h file and still change MEDIAN_MAX_SIZE size in it's class?

Change it in RunningMedian.h, if RunningMedian.cpp is separately compiled into an object file then it won't see your re-definition if you place it somewhere else. — Patrick Trentin
– Patrick Trentin, Commented Feb 10, 2017 at 6:27

Alex Zywicki · Accepted Answer · 2017-02-10 03:51:14Z

4

You can #undef MEDIAN_MAX_SIZE and the redefine it, like this:

#ifdef MEDIAN_MAX_SIZE //if the macro MEDIAN_MAX_SIZE is defined 
#undef MEDIAN_MAX_SIZE //un-define it
#define MEDIAN_MAX_SIZE 30//redefine it with the new value
#endif

You may want to redefine it to its original value after you are done using it with your adjusted value, just in case something else depends on that value being the original.

answered Feb 10, 2017 at 3:51

Alex Zywicki

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1 Comment

Patrick Trentin Over a year ago

@user1213320 Perhaps it is worth mentioning that this code needs to appear right after the first definition, otherwise the old value might be used somewhere else before being redefined. e.g. RunningMedian.cpp might be separately compiled before the header file containing the re-definition is ever included, therefore it will use the old values

dmaixner · Accepted Answer · 2020-02-06 11:28:39Z

4

I think it should be possible to create new header file (e.g. MyRunningMedian.h) in your project, containing just your changed definitions:

#ifndef MEDIAN_MAX_SIZE
#define MEDIAN_MAX_SIZE     30
#endif

Then, you need to pass this header file to preprocessor, to include it as a first #include for the RunningMedian. You can do this by using -include directive, see https://gcc.gnu.org/onlinedocs/gcc/Preprocessor-Options.html.

E.g. in PlatformIO you can do it in platformio.ini this way:

[common]
build_flags = 
    -include "include/MyRunningMedian.h"

answered Feb 6, 2020 at 11:28

dmaixner

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Comments

Community · Accepted Answer · 2017-05-23 12:33:40Z

3

Alex Zywicki's answer is perfect for cases where it doesn't matter if you redefine the macro. But, to be safe or if you need to ensure the macro gets defined back to its previous definition, you can use the push_macro and pop_macro pragmas (assuming your compiler supports it):

#ifdef MEDIAN_MAX_SIZE
#pragma push_macro("MEDIAN_MAX_SIZE")
#define MEDIAN_MAX_SIZE 30

// Use the modified value for MEDIAN_MAX_SIZE here

#pragma pop_macro("MEDIAN_MAX_SIZE")

This allows you to temporarily redefine macros for a block of code.

edited May 23, 2017 at 12:33

CommunityBot

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answered Feb 10, 2017 at 13:43

Jeffrey Cash

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