#ifdef HAVE_PROTOTYPES
#define JMETHOD(type,methodname,arglist) type (*methodname) arglist
#else
#define JMETHOD(type,methodname,arglist) type (*methodname) ()
#endif
typedef JMETHOD(boolean, jpeg_marker_parser_method, (j_decompress_ptr cinfo));
--->typedef boolean (* jpeg_marker_parser_method) (j_decompress_ptr cinfo);即函数指针
typedef struct jpeg_decompress_struct * j_decompress_ptr;
函数指针模块化声明方法
原文：http://www.cnblogs.com/black-mamba/p/6371943.html
