proto_header.h

SIP（Session Initiation Protocol）是由IETF定义

/* Add: Apple Mac OS X Support */
#if !defined(__FreeBSD__) || !defined(__APPLE__)
 #define __P(protos) protos

 #ifdef __cplusplus
  #define __BEGIN_DECLS extern "C" {
  #define __END_DECLS }
 #else
  #define __BEGIN_DECLS
  #define __END_DECLS
 #endif

#else
 #include <sys/cdefs.h>
#endif