Freestanding (C++ implementation)

In a hosted implementation, the program requires the entry point to be a global function called main(), while in a freestanding implementation it is implementation-defined. While _start() is typically the general default for the entry point function in many environments, this may be overridden. Under a hosted implementation, a C++ program is required to support concurrently executing threads, while in a freestanding implementation, this is implementation defined. Under a freestanding implementation, the predefined macro __STDC_HOSTED__ will always expand to 0, while being expanded to 1 in hosted implementations. == Header set ==

Although the header set of a freestanding implementation is implementation defined, the following headers are at least required for a freestanding implementation, partially and fully: Although not standard, some compilers like GCC and Clang partially support and headers in freestanding implementations, while Clang also provides header . Even though declarations of runtime allocator operator new is optional, transient constexpr allocations (by new/delete) and operator delete are still required for freestanding implementations. Newer proposals like P3295R3 suggest allowing containers like std::vector and allocators like std::allocator to be allowed at freestanding implementations only in transient constexpr allocations. ==See also==