Controls whether or not a header file can be included more than once in the same source file.
#pragma once [ on ]
Use this pragma to ensure that the compiler includes header files only once in a source file.
There are two versions of this pragma: #pragma once and #pragma once on. Use #pragma once in a header file to ensure that the header file is included only once in a source file. Use #pragma once on in a header file or source file to insure that any file is included only once in a source file.
This pragma does not correspond to any setting in the Language panel. By default, this pragma is disabled.