What does it mean when the function in global namespace is declared as static C++? [duplicate]

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Possible Duplicate:
What is a “static” function?

I have seen a function in a global namespace that is declared like this:

static int function_name(int a, double* p, int c, float * u)
{
     //do something with these arguments
}

What the static keyword means here?

EDIT: Now when I know what is for static, please explain what advantage gives the restriction of a function to be visible in a file only where it is declared? I mean why I should restrict my function visibility, what it gives to me?

来源：https://stackoverflow.com/questions/5300627/what-does-it-mean-when-the-function-in-global-namespace-is-declared-as-static-c