#define ZEND_VERIFY_RESOURCE(rsrc) \
if (!rsrc) { \
RETURN_FALSE; \
}
#define ZEND_FETCH_RESOURCE(rsrc, rsrc_type, passed_id, default_id, resource_type_name, resource_type) \
rsrc = (rsrc_type) zend_fetch_resource(passed_id TSRMLS_CC, default_id, resource_type_name, NULL, 1, resource_type); \
ZEND_VERIFY_RESOURCE(rsrc);
#define ZEND_FETCH_RESOURCE2(rsrc, rsrc_type, passed_id, default_id, resource_type_name, resource_type1, resource_type2) \
rsrc = (rsrc_type) zend_fetch_resource(passed_id TSRMLS_CC, default_id, resource_type_name, NULL, 2, resource_type1, resource_type2); \
ZEND_VERIFY_RESOURCE(rsrc);
#define ZEND_REGISTER_RESOURCE(rsrc_result, rsrc_pointer, rsrc_type) \
zend_register_resource(rsrc_result, rsrc_pointer, rsrc_type);
#define ZEND_GET_RESOURCE_TYPE_ID(le_id, le_type_name) \
if (le_id == 0) { \
le_id = zend_fetch_list_dtor_id(le_type_name); \
}
我们由mysql_connect函数返回的其实是一个link id（resource(4) of type (mysql link)），通过ZEND_FETCH_RESOURCE和ZEND_FETCH_RESOURCE2宏，可以映射到对应的mysql资源上去。这两个宏都调用了zend_fetch_resource方法，所以下面我们看下这个方法。
ZEND_API void *zend_fetch_resource(zval **passed_id TSRMLS_DC, int default_id, char *resource_type_name, int *found_resource_type, int num_resource_types, ...)
比如在mysql_list_dbs函数中调用ZEND_FETCH_RESOURCE2宏：
ZEND_FETCH_RESOURCE2(mysql, php_mysql_conn *, mysql_link, id, "MySQL-Link", le_link, le_plink);
其中mysql保存了返回的有效资源，php_mysql_conn *定义了返回资源的类型，mysql_link, id分别对应着passed_id 和 default_id（因为很多函数调用，不传入具体的conn，就是使用default值），"MySQL-Link"是resource_type_name，le_link, le_plink是zend_fetch_resource的...部分，它们俩是static int类型的值。
由zend_fetch_resource可以看出，resource(4) of type (mysql link)的value.lval中包含了long型的id。如果default_id为-1，那么就是用passed_id传入的id，否则就使用default_id作为id，利用zend_list_find来寻找其对应的资源。
看了几个函数之后，其实该扩展也就是对mysql提供的c接口的封装而已。但是封装的很规范也很稳定！
如果想了解进一步，那还是得看MYSQL的源代码。下面贴了几个重要的数据结构。
-----------------------------------------
一些对于查错可能有用的php函数：
复制代码 代码如下:
error_reporting(E_ALL);
#var_dump(mysql_get_host_info($conn));
#var_dump(mysql_get_proto_info($conn));
#var_dump(mysql_get_server_info($conn));
#var_dump(mysql_stat($conn));
#var_dump(mysql_errno($conn));
#var_dump(mysql_error($conn));
#var_dump(mysql_info($conn));
--------------------------------------------
MYSQL源码中一些有用的struct
复制代码 代码如下:
typedef struct st_mysql
{
NET net; /* Communication parameters */
gptr connector_fd; /* ConnectorFd for SSL */
char *host,*user,*passwd,*unix_socket,*server_version,*host_info,*info;
char *db;
struct charset_info_st *charset;
MYSQL_FIELD *fields;
MEM_ROOT field_alloc;
my_ulonglong affected_rows;
my_ulonglong insert_id; /* id if insert on table with NEXTNR */
my_ulonglong extra_info; /* Not used */
unsigned long thread_id; /* Id for connection in server */
unsigned long packet_length;
unsigned int port;
unsigned long client_flag,server_capabilities;
unsigned int protocol_version;
unsigned int field_count;
unsigned int server_status;
unsigned int server_language;
unsigned int warning_count;
struct st_mysql_options options;
enum mysql_status status;
my_bool free_me; /* If free in mysql_close */
my_bool reconnect; /* set to 1 if automatic reconnect */
/* session-wide random string */
char scramble[SCRAMBLE_LENGTH+1];
/*
Set if this is the original connection, not a master or a slave we have
added though mysql_rpl_probe() or mysql_set_master()/ mysql_add_slave()
*/
my_bool rpl_pivot;
/*
Pointers to the master, and the next slave connections, points to
itself if lone connection.
*/
struct st_mysql* master, *next_slave;
struct st_mysql* last_used_slave; /* needed for round-robin slave pick */
/* needed for send/read/store/use result to work correctly with replication */
struct st_mysql* last_used_con;
LIST *stmts; /* list of all statements */
const struct st_mysql_methods *methods;
void *thd;
/*
Points to boolean flag in MYSQL_RES or MYSQL_STMT. We set this flag
from mysql_stmt_close if close had to cancel result set of this object.
*/
my_bool *unbuffered_fetch_owner;
#if defined(EMBEDDED_LIBRARY) || defined(EMBEDDED_LIBRARY_COMPATIBLE) || MYSQL_VERSION_ID >= 50100
/* needed for embedded server - no net buffer to store the 'info' */
char *info_buffer;
#endif
} MYSQL;
typedef struct st_mysql_methods
{
my_bool (*read_query_result)(MYSQL *mysql);
my_bool (*advanced_command)(MYSQL *mysql,
enum enum_server_command command,
const char *header,
unsigned long header_length,
const char *arg,
unsigned long arg_length,
my_bool skip_check,
MYSQL_STMT *stmt);
MYSQL_DATA *(*read_rows)(MYSQL *mysql,MYSQL_FIELD *mysql_fields,
unsigned int fields);
MYSQL_RES * (*use_result)(MYSQL *mysql);
void (*fetch_lengths)(unsigned long *to,
MYSQL_ROW column, unsigned int field_count);
void (*flush_use_result)(MYSQL *mysql);
#if !defined(MYSQL_SERVER) || defined(EMBEDDED_LIBRARY)
MYSQL_FIELD * (*list_fields)(MYSQL *mysql);
my_bool (*read_prepare_result)(MYSQL *mysql, MYSQL_STMT *stmt);
int (*stmt_execute)(MYSQL_STMT *stmt);
int (*read_binary_rows)(MYSQL_STMT *stmt);
int (*unbuffered_fetch)(MYSQL *mysql, char **row);
void (*free_embedded_thd)(MYSQL *mysql);
const char *(*read_statistics)(MYSQL *mysql);
my_bool (*next_result)(MYSQL *mysql);
int (*read_change_user_result)(MYSQL *mysql, char *buff, const char *passwd);
int (*read_rows_from_cursor)(MYSQL_STMT *stmt);
#endif
} MYSQL_METHODS;
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