To guarantee that the header is processed only once in a given source file, we start by testing the #ifndef.

为了保证头文件在给定的源文件中只处理过一次，我们首先检测 #ifndef。

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REPHEADER: report header; displayed once only at the beginning of the report.

报表页眉；只在报表的开始处显示一次。

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The header files are modified only rarely during the scope of a project.

在一个项目的范围内，很少对头文件进行修改。

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Rising highest to meet Danny Williams' free-kick, Wright could only direct his header across and wide of goal from six yards.

BBC: Hereford 2-1 Farnborough

Wales were still showing their teeth on the counter and Joe Ledley was unfortunate he could only direct a header at Akinfeev after good work from Ricketts.

BBC: Wales 1-3 Russia

Eren Derdiyok came close to equalising in the first half but could only direct his header from Tranquillo Barnetta's left-wing cross straight at Hertha goalkeeper Jaroslav Drobny.

CNN: Ramos denies Leverkusen