#pragma once is accepted for compatibility with other compilers, and enables you to use other forms of header guard coding. However, Arm recommends using #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.