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I have a class which has a static const array, it has to be initialized outside the class: 

class foo{  
static const int array[3];  
};    
const int foo::array[3] = { 1, 2, 3 };

But then I get a duplicate symbol foo::array in foo.o and main.o foo.o hold the foo class, and main.o holds main() and uses instances of foo.
How can I share this static const array between all instances of foo? I mean, that's the idea of a static member.

Petruza
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1 Answers1

10

Initialize it in your corresponding .cpp file not your .h file.

When you #include it's a pre-processor directive that basically copies the file verbatim into the location of the #include. So you are initializing it twice by including it in 2 different compilation units.

The linker sees 2 and doesn't know which one to use. If you had only initialized it in one of the source files, only one .o would contain it and you wouldn't have a problem.

Brian R. Bondy
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  • Yes, right. Thanks! I keep making this dumb errors with header files and getting linker errors. – Petruza May 24 '10 at 13:37
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    I had a question regarding this - Why don't header guards resolve the problem? -- Thanks, Sid. – Opt Jul 11 '10 at 00:42
  • Header guards only work within the scope of a compilation unit, such as a .cpp file. If you've got multiple .cpp files in your project then each one is compiled as a separate unit. If they include the same header then it will be included one for each .cpp file, thus the symbol will be multiply defined. – Sean Sep 27 '11 at 15:13