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Asked: 2026-05-16T17:05:12+00:00

in this code: int foo() { static int x; } is the x global

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in this code:

int foo() {
   static int x;
}

is the x global to all threads or local in each thread? Or does that depends on a compiler flag and/or the compiler, so I cannot really know what it is from the code?

Several questions (all of them independent from compiler and compiler flags and OS):

  1. How can I create a static variable which is global to all threads?
  2. How can I create a static variable which is local to each thread?
  3. How can I create a global variable which is global to all threads?
  4. How can I create a global variable which is local to each thread?

I guess that this is not in C++ itself. (Is it in C++0x?) Some Boost lib which can do this?

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1 Answer

  1. Editorial Team

    x is global to all threads. Always, independent of compiler and/or its flags. Independent of whether this is in C++11 or C++03. So if you declare a regular global or static local variable, it will be shared between all threads.
    In C++11 we will have the thread_local keyword. Until then, you can use thread_specific_ptr from Boost.Thread.

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