This pragma enables the compiler to skip subsequent includes of that header file.
#pragma once is accepted for compatibility with other compilers, and
enables you to use other forms of header guard coding. However, it is preferable to use
#ifndef and #define coding because this is more
portable.
Examples
The following example shows the placement of a #ifndef guard around the
body of the file, with a #define of the guard variable after the
#ifndef.
#ifndef FILE_H
#define FILE_H
#pragma once // optional
... body of the header file ...
#endif
The #pragma once is marked as optional in this example. This is because
the compiler recognizes the #ifndef header guard coding and skips
subsequent includes even if #pragma once is absent.
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