C++ #include and #import difference
C++Visual C++GccImportIncludeC++ Problem Overview
What is the difference between #include and #import in C++?
C++ Solutions
Solution 1 - C++
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.
Solution 2 - C++
#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.
Solution 3 - C++
#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.
Solution 4 - C++
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...
Solution 5 - C++
Please note that in gcc 4.1, #import is deprecated. If you use it, you will get warning:
>#import is a deprecated GCC extension
Solution 6 - C++
Should this post be updated?
Now, since the C++20 standard is outta there, we can get into scope "modules" with the import statement.
https://en.cppreference.com/w/cpp/language/modules
In terms of compiling speed when multiple modules are called from different parts of the code, import statement seems to be quicker than the old #include preprocesor directive.