About Static Variable and Thread-Safe

I was asked to write a function with a static variable in it. for example:

Code:

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void foo(){
static int a=1;
a++;
}

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Obviously this is not thread safe. Then I was asked to solve this problem to make it thread safe.
I was told that I can use a class to wrap it. Does anybody has an idea what that is?

Do you have a better solution?

think about why it isn't thread safe? what can you do to fix that?

If you don't know what a class is, consider learning that before you tackle thread synchronization.....