What is declspec and when do I need to use it

Question

I have seen instances of   declspec in the code that I am reading  What is it  And when would I need to use this construct

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I know it s been eight years but I wanted to share this piece of code found in MRuby that shows how   declspec   can bee used at the same level as the export keyword       Declare a public MRuby API function      if defined MRB BUILD AS DLL   if defined MRB CORE     defined MRB LIB    define MRB API   declspec dllexport   else   define MRB API   declspec dllimport   endif  else   define MRB API extern  endif

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Another example to illustrate the   declspec keyword   When you are writing a Windows Kernel Driver  sometimes you want to write your own prolog epilog code sequences using inline assembler code  so you could declare your function with the naked attribute     declspec  naked   int func  formal parameters        Or   define Naked   declspec  naked   Naked int func  formal parameters        Please refer to naked  C

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Essentially  it s the way Microsoft introduces its C   extensions so that they won t conflict with future extensions of standard C    With   declspec  you can attribute a function or class  the exact meaning varies depending on the nature of   declspec    declspec naked   for example  suppresses prolog epilog generation  for interrupt handlers  embeddable code  etc     declspec thread  makes a variable thread-local  and so on   The full list of   declspec attributes is available on MSDN  and varies by compiler version and platform

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It is mostly used for importing symbols from   exporting symbols to a shared library  DLL   Both Visual C   and GCC compilers support   declspec dllimport  and   declspec dllexport   Other uses  some Microsoft-only  are documented in the MSDN

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This is a Microsoft specific extension to the C   language which allows you to attribute a type or function with storage class information    Documentation    declspec  C

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The canonical examples are   declspec dllimport  and   declspec dllexport   which instruct the linker to import and export  respectively  a symbol from or to a DLL      header   declspec dllimport  void foo         code - this calls foo   somewhere in a DLL foo         declspec     just wraps up Microsoft s specific stuff - to achieve compatibility  one would usually wrap it away with macros

[c++] What is __declspec and when do I need to use it?

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