'pragma' is used to express implementation dependent preprocessor statements. The idea, the use of 'once' that is, (as far as I know) is specific to the compiler that Visual Studio uses. Such a technique isn't portable if you wanted to jump to a different compiler.
It is a far, far better idea to use header guards (defining a macro constant and testing for its existence) because all parts of the construct are standard compliant.
With respect to whether you should use it everywhere take a look at translation units and use the '/C' and '/P' flags for cl.exe; that spits out a pre-processed source file. Really the idea only needs to be used in header files because they are the only things that should really be 'included'.
There's no harm in using it in every file. In fact it probably makes your life easier in the long run in case you start re-adding the file elsewhere. That said, if you can guarantee you'll never include the file in another header then you can leave it out because it's not needed. Like I said though, probably easier to just get into the habbit of guarding every header for the delayed convenience.
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#1BinaryPhysics
Posted 28 September 2012 - 04:32 PM
'pragma' is used to express implementation dependent preprocessor statements. The idea (as far as I know) is specific to the compiler that Visual Studio uses. Such a technique isn't portable if you wanted to jump to a different compiler.
It is a far, far better idea to use header guards (defining a macro constant and testing for its existence) because all parts of the construct are standard compliant.
With respect to whether you should use it everywhere take a look at translation units and use the '/C' and '/P' flags for cl.exe; that spits out a pre-processed source file. Really the idea only needs to be used in header files because they are the only things that should really be 'included'.
There's no harm in using it in every file. In fact it probably makes your life easier in the long run in case you start re-adding the file elsewhere. That said, if you can guarantee you'll never include the file in another header then you can leave it out because it's not needed. Like I said though, probably easier to just get into the habbit of guarding every header for the delayed convenience.
It is a far, far better idea to use header guards (defining a macro constant and testing for its existence) because all parts of the construct are standard compliant.
With respect to whether you should use it everywhere take a look at translation units and use the '/C' and '/P' flags for cl.exe; that spits out a pre-processed source file. Really the idea only needs to be used in header files because they are the only things that should really be 'included'.
There's no harm in using it in every file. In fact it probably makes your life easier in the long run in case you start re-adding the file elsewhere. That said, if you can guarantee you'll never include the file in another header then you can leave it out because it's not needed. Like I said though, probably easier to just get into the habbit of guarding every header for the delayed convenience.