#pragma & #pragma once usage

[King Of CPP]

Hi , I don't have any Ideas about what these preprocessors will do. Can anyone please explain ?


Thanks.

[goldenchicken]

#pragma once does exactly the same as creating header guards, however, pragma is not supported by all compilers.
If you need a reminder of what header guards are:

Header guards prevent a file from being included in the same file more than once.

//file.h
#ifndef FILENAME_H
#define FILENAME_H
//code here
#endif

//main.cpp
#include "file.h" //includes the code between #ifndef en #endif
#include "file.h" //includes nothing, as FILENAME_H is already defined and the #ifndef evaluates false 

I recommend using regular header guards rather than #pragma once, because, as I already said, pragma isn't supported by all compilers.

If anything is still unclear feel free to ask me

[keskiverto]

Haven't used them much, so:

http://www.cplusplus.com/doc/tutorial/preprocessor/
http://www.cplusplus.com/articles/Gw6AC542/

[Handy Andy]

Hello King Of CPP,

You may find this line useful. I use it quite often.

https://msdn.microsoft.com/en-us/library/d9x1s805.aspx

Hope that helps,

Andy