It is a macro. Something like this can be found by googling:
Code:
> #ifdef USINGDLL
> #if defined(WIN32)
> /* Visual C/C++, Borland, MinGW and Watcom */
> #if defined(__VISUALC__) || defined(_MSC_VER) ||
> defined(__BORLANDC__) || defined(__GNUC__) || defined(__WATCOMC__)
> #define PLDLLEXPORT __declspec(dllexport)
> #define PLDLLIMPORT __declspec(dllimport)
> #else
> #define PLDLLEXPORT
> #define PLDLLIMPORT
> #endif
> #elif defined(__CYGWIN__)
> #define PLDLLEXPORT __declspec(dllexport)
> #define PLDLLIMPORT __declspec(dllimport)
> #elif defined(__GNUC__) && __GNUC__ > 3
> /* Follow ideas in http://gcc.gnu.org/wiki/Visibility for GCC
> version 4.x
> * The following forces exported symbols specifically designated
> with
> * PLDLLEXPORT to be visible. */
> #define PLDLLEXPORT __attribute__ ((visibility("default")))
> #define PLDLLIMPORT
> #endif
> #endif