Dear All,

Can you tell me the way to declare global variables (only once) in a Psoc 5 project that contain many sub routines files ?

I tried to create a single .h file containing all the global variables and include him into each sub files, but the compiler seems to not be happy with this solution.

Is there a proper way to do that ?

Thank you,

JP

You write

 extern int value;

in the header file, which you then include in all place where you need access to the value. Then you write

 int value=0;

in just one C-file. That way, the variable gets defined only once, and not multiple times. For a complete explanation, see here

Thank you infinitely for the answer !

I have already used the "extern" keyword but your link gave me the good way to use only one header file with him.

Thank you again  

JP

Actually you don't need to use a single header file. The 'extern' statement is to declare the variable, so the compiler knows that it exists. Since include files are just that - text-based includes - it doesn't matter how many of them you have containing this declaration.

Whats important is that you have exactly one definition of the variable (this is, the line without 'extern'), because that is the place which defines how the variable really looks like, and reserver the space in memory for storing it. YOu will get a linker error when you have multiple definitions.

Having dais that, it still is advisable and good practice to use only a single header file. That way you ensure the declaration is always the same. Also, one can see the dependencies between different parts of the code.

I feel it's the time to say something about header-files.

Header-files ( .h ) usually contain "declarations" only, no definitions. Thus only the compiler is told about some new objects to come. >very often used to declare prototypes of functions, typedefs and structures that must be known to the calling ( main() ) program.

So accidently there can pop-up an errormessage when you #include the same file in several places within your project stating that something is defined more than once.

There is a standard way out of this and commonly used (though not as commonly known) by C programmers:

A  .h-file usually starts with the lines

#ifndef mysymbol // __Filename_h would be a very good value for mysymbol since it has to be unique within the project

#define mysymbol // now the preprocessor "knows" this file has been included

// here goes the .h-file body

#endif

Happy coding

Bob

Hello guys,

Thank you for all of your valuable answers.

Following the link of Hli, I have used a .h file for definition and declaration of my global variables :

#ifdef DEFINE_VARIABLES

#define EXTERN

#else

#define EXTERN extern

#endif

EXTERN type myvariable1

EXTERN type myvariable2

The "DEFINE_VARIABLES" keyword, help to switch between definition and declaration of the variables.

Naturally, one can extend (and bulletproof) the method with more pragma directives (see above link from Hli) but I am already happy with these few lines because, now, I have just to change / add variable(s) in one single file.

JP

and for a header file named global.h, an improvement will be maybe :

#undef

EXTERN

#ifndef

EXTERN type myvariable

That's a good idea, but it will fail when the variable is initialized as

EXTERN uint8 MyVar = 27;

Bob

Always following the link from Hli :

Argh, the previous post is completely wrong