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extern "C" 與 __cplusplus 安全使用

無意中看原始碼看到的程式碼風格 如果已經巨集定義 __cplusplus 則加入extern "C" 檔案目錄為/usr/include/event2/http_struct.h

#ifndef _EVENT2_HTTP_STRUCT_H_
#define _EVENT2_HTTP_STRUCT_H_

/** @file event2/http_struct.h

  Data structures for http.  Using these structures may hurt forward
  compatibility with later versions of Libevent: be careful!

 */

#ifdef __cplusplus
extern "C" {
#endif

#include <event2/event-config.h>
#ifdef _EVENT_HAVE_SYS_TYPES_H
#include <sys/types.h>
#endif
#ifdef _EVENT_HAVE_SYS_TIME_H
#include <sys/time.h>
#endif

/* For int types. */
#include <event2/util.h>

/**
 * the request structure that a server receives.
 * WARNING: expect this structure to change.  I will try to provide
 * reasonable accessors.
 */
struct evhttp_request {
#if defined(TAILQ_ENTRY)
	TAILQ_ENTRY(evhttp_request) next;
#else
struct {
	struct evhttp_request *tqe_next;
	struct evhttp_request **tqe_prev;
}       next;
#endif

	/* the connection object that this request belongs to */
	struct evhttp_connection *evcon;
	int flags;
/** The request obj owns the evhttp connection and needs to free it */
#define EVHTTP_REQ_OWN_CONNECTION	0x0001
/** Request was made via a proxy */
#define EVHTTP_PROXY_REQUEST		0x0002
/** The request object is owned by the user; the user must free it */
#define EVHTTP_USER_OWNED		0x0004
/** The request will be used again upstack; freeing must be deferred */
#define EVHTTP_REQ_DEFER_FREE		0x0008
/** The request should be freed upstack */
#define EVHTTP_REQ_NEEDS_FREE		0x0010

	struct evkeyvalq *input_headers;
	struct evkeyvalq *output_headers;

	/* address of the remote host and the port connection came from */
	char *remote_host;
	ev_uint16_t remote_port;

	/* cache of the hostname for evhttp_request_get_host */
	char *host_cache;

	enum evhttp_request_kind kind;
	enum evhttp_cmd_type type;

	size_t headers_size;
	size_t body_size;

	char *uri;			/* uri after HTTP request was parsed */
	struct evhttp_uri *uri_elems;	/* uri elements */

	char major;			/* HTTP Major number */
	char minor;			/* HTTP Minor number */

	int response_code;		/* HTTP Response code */
	char *response_code_line;	/* Readable response */

	struct evbuffer *input_buffer;	/* read data */
	ev_int64_t ntoread;
	unsigned chunked:1,		/* a chunked request */
	    userdone:1;			/* the user has sent all data */

	struct evbuffer *output_buffer;	/* outgoing post or data */

	/* Callback */
	void (*cb)(struct evhttp_request *, void *);
	void *cb_arg;

	/*
	 * Chunked data callback - call for each completed chunk if
	 * specified.  If not specified, all the data is delivered via
	 * the regular callback.
	 */
	void (*chunk_cb)(struct evhttp_request *, void *);
};

#ifdef __cplusplus
}
#endif

#endif /* _EVENT2_HTTP_STRUCT_H_ */