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How to work with a variable in a namespace

I think I have a fundamental misunderstanding of the namespace and / or static variable. But I tried this test code (typed manually, forgive typos)

test.h:

namespace test{
   static int testNum=5;
   void setNum(int value);
}

main.cpp:

#include <test.h>

int test::setNum(int value){
   testNum=value;
}

int main(){
    test::setNum(9);
    cout<<test::testNum;
}

when I run this, I get a value of 5, not 9, as I expected. It seems almost as if I had two instances of the testNum variable, but this seems to be the exact opposite of what static should do. I suppose I made a mistake in assuming that these functions were identical to their equivalent java equvilants ...

I also get an error message indicating that testNum is declared multiple times if I remove the statics from my testNum declaration, can anyone explain why this is so?

thank

+5
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#include <iostream>
using namespace std;

namespace test{
   static int testNum=5;
   void setNum(int value);
}

void test::setNum(int value){
   testNum=value;
}

int main(){
    test::setNum(9);
    cout<<test::testNum;
}

:

$ ./a.out 
9

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+1
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