#include .h and extern

hello       

i'm newbies in ide arduino
 
file .ino

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#include ex.h

const int = 0 ;

foo snmp ;

void setup() {
  // put setup code here, run once:

}

void loop() {
  // put main code here, run repeatedly:
 snmp.test () ;
}



file ex.h

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#ifndef ex_h
#define ex_h


class foo {
 void test () ;
} ;

#endif



file ex.cpp

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#include <arduino.h>

 void foo::test {
  = 0 ;  <--- error " not delared in scope "
 }



in c++ , use extern in .h off project ..
with project .ino

thank lot !!!!

there many things wrong here don't know start....

let's start here:

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#include ex.h

that's not how include something. try

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#include "ex.h"


next, ex.cpp needs include ex.h.

and ex.h needs include arduino.h

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void foo::test {

is not how define function. try

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void foo::test(){



and because it's private , declare in ex.h

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public:
  void foo::test();


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const int = 0 ;
//....
a = 0 ;

how think can assign value const? that's whole idea of const, can't...

then off more complex matters. ex.cpp compiled separate of file.ino. has therefor no knowledge it's use in file.ino , variables there. if want indeed change variable on there need tell compiler exist putting in ex.h

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extern int a; //and have make a int instead of const int because can never work.


but really, why want this. it's ugly way of doing it. class can work on single variable a, no matter how many objects of class foo have. , relies on declaring variable in sketch. why not part of object? in ex.h

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class foo {
  public:
    void test ();
  protected:
    int a; //which needs better name
} ;


and if want variable in sketch (because variable has no 1 1 relation object, pass reference. google see means

in ex.h

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class foo {
 public:
   void test (int& a) ;
} ;

in ex.cpp

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void foo::test(int& a) {
  a = 0 ;
}


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