How to access a static variable from another file in C?

Question

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Static variable

How to access a static variable from another file in C? As a Static variable has a file scope, I think there is no way we can access it outside a file. But still I feel there might be some trick or way to do the same.

Solution 1

I don't think there is a easy way. If you can change the file with the static variable you can do something like:

static int hiddenVar; // The static var you want to get at

// A new function you write
int * getHiddenVar() {
   return &hiddenVar;
}

But of course if you can change the file, you would just drop the static keyword.

Also, I doubt this helps, but I've had to do something like this when writing a kernel module in FreeBSD. I used a trick where I called the kernel's linker functions to find the address of a static function. I doubt you can do this in a normal C program though.

Solution 2

Use the extern keyword in your declaration to specify that the variable comes from another file (external linkage). Drop the static keyword in your original definition.

The external vs. internal linkage thing is explained in this article.

Solution 3

You can only do this indirectly, e.g. if a function within the scope of the file containing the static variable passes you a pointer to it.

Comments

[Alok Singhal]

Umm. What? A variable that has both internal and external linkage?

[Thorsten79]

I clarified the declaration vs. definition part.

[Alok Singhal]

Now your answer is technically correct, but doesn't answer the question, unfortunately. The question itself isn't that good though.