C++ include and import difference
-
05-07-2019 - |
Question
What is the difference between #include
and #import
in C++?
Solution
#import
is a Microsoft-specific thing, apparently for COM or .NET stuff only.
#include
is a standard C/C++ preprocessor statement, used for including header (or occasionally other source code) files in your source code file.
OTHER TIPS
Import in VC++: #import
is for type libraries or .tlbs (COM stuff).
The content of the type library is converted into C++ classes, mostly describing the COM interfaces for you automatically, and then it is included into your file.
The #import
directive was introduced by Microsoft as an extension to the C++ language. You can read about it at this MSDN article.
The #import
directive is also used with .NET / CLI stuff.
Import in gcc:
The import in gcc is different from the import in VC++. It is a simple way to include a header at most once only. (In VC++ and GCC you can do this via #pragma
once as well)
The #import
directive was officially undeprecated by the gcc team in version 3.4 and works fine 99% of the time in all previous versions of gcc which support
Include: #include
is for mostly header files, but to prepend the content to your current file. #include
is part of the C++ standard. You can read about it at this MSDN article.
#import
is overall a solution to the usual
#ifndef ...
#define ...
#include ...
#endif
work-around. #import
includes a file only if it hasn't been included before.
It might be worth noting that Apple's Objective-C also uses #import
statements.
import was also one of the keywords associated with n2073, Modules in C++, proposed to the language committee by Daveed Vandevoorde in September 2006. I'm not enough of a language geek to know if that proposal was definitively shelved or if it's awaiting an implementation (proof of concept) from the author or someone else...
Please note that in gcc 4.1, #import
is deprecated. If you use it, you will get warning:
#import
is a deprecated GCC extension