Like Visual C++, GCC also comes with a set of built-in atomic functions. These differ based on the underlying architecture that the GCC version and the standard library one uses. Since GCC is used on a considerably larger number of platforms and operating systems than VC++, this is definitely a big factor when considering portability.
For example, not every built-in atomic function provided on the x86 platform will be available on ARM, partially due to architectural differences, including variations of the specific ARM architecture. For example, ARMv6, ARMv7, or the current ARMv8, along with the Thumb instruction set, and so on.
Before the C++11 standard, GCC used __sync-prefixed extensions for atomics:
type __sync_fetch_and_add (type ...
