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Zitat von »"Deviloper"«

Ball.h

	C-/C++-Quelltext
1 2 3 4 5 6	#if !defined(BALL_H__INCLUDED) #define BALL_H__INCLUDED #if (_MSC_VER > 1000) #pragma once #endif // _MSC_VER > 1000

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Zitat von »"Das Gurke"«

Wenn mans umdreht machts vllt Sinn. Bei wirklich riesigen Projekten könnte das compiletime sparen Obwohl ich net glaube, das das so ins Gewicht fällt.

Zitat

"#pragma once" is just an optimization issue. If a file is included a second time in the same TU, a dumb compiler will re-open it and give it to the preprocessor who strips its contents entirely because the include guard is already defined. Re-opening + preprocessing takes little but significant time.

With the "#pragma once" the programmer just gives an hint to the compiler that re-opening is unnecessary and ignores the #include directive immediately. You see, there *is* a speed gain even in the presence of canonical include guards.

Of course, a smarter compiler like g++ will recognize the canonical include guards and deduce that re-opening is unnecessary without any explicit hint given by the programmer.