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RE: program executin times differ between gcc versions
> If you have variables that might be modified by multiple threads you should declare them as volatiles in order to prevent compiler optmization and wrong execution.
NOTE: the "volatile" qualifying keyword by itself does not prevent problems with multiple threads modifying the variable concurrently.
Neither C nor C++ have language support for multiple threads. (There are "bolt-on" threading libraries, but that's not the same as multiple threads being supported by the language -- "volatile" is orthogonal to resolving issues due to multiple threads.)