這個額外的關鍵字在這個 C++ 類聲明中是什么意思？

Question

我正在查看一些聲明如下類的 C++ 代碼：

class LIBSBML_EXTERN LayoutModelPlugin : public SBasePlugin

LIBSBML_EXTERN 關鍵字的用途是什么？

Answer 1

這是一個宏。 我不確定您正在使用哪些庫，但可能是您可以在此處看到的定義的宏： https : //github.com/copasi/copasi-dependencies/blob/master/src/libSBML/src/ sbml/common/extern.h

#if ( ! defined LIBSBML_STATIC )
/**
 * The following ifdef block is the standard way of creating macros which
 * make exporting from a DLL simpler. All files within this DLL are
 * compiled with the LIBSBML_EXPORTS symbol defined on the command line.
 * This symbol should not be defined on any project that uses this
 * DLL. This way any other project whose source files include this file see
 * LIBSBML_EXTERN functions as being imported from a DLL, wheras this DLL
 * sees symbols defined with this macro as being exported.
 *
 * (From Andrew Finney's sbwdefs.h, with "SBW" replaced by "LIBSBML" :)
 */
#if defined(LIBSBML_EXPORTS)
#  define LIBSBML_EXTERN __declspec(dllexport)
#else
#  define LIBSBML_EXTERN __declspec(dllimport)
#endif

#else
#  define LIBSBML_EXTERN
#endif  /* LIBSBML_STATIC */

如果需要，它用於將類定義與 DLL 接口。

Answer 2

它是一個宏，您可以這樣定義：

#define LIBSBML_EXTERN whatever

其中， whatever是什么樣的編譯器看跌期權代替LIBSBML_EXTERN編譯之前。