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4.2 #pragma once

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.

Example

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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