MYSQL 数据结构 和MYSQL_RES

以下代码块是用来连接数据库的通讯过程，要连接MYSQL，必须建立MYSQL实例，通过mysql_init初始化方能开始进行连接.

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,*db;

  unsigned int  port,client_flag,server_capabilities;

  unsigned int  protocol_version;

  unsigned int  field_count;

  unsigned int  server_status;

  unsigned long thread_id;      /* Id for connection in server */

  my_ulonglong affected_rows;

  my_ulonglong insert_id;       /* id if insert on table with NEXTNR */

  my_ulonglong extra_info;              /* Used by mysqlshow */

  unsigned long packet_length;

  enum mysql_status status;

  MYSQL_FIELD   *fields;

  MEM_ROOT      field_alloc;

  my_bool       free_me;        /* If free in mysql_close */

  my_bool       reconnect;      /* set to 1 if automatic reconnect */

  struct st_mysql_options options;

  char          scramble_buff[9];

  struct charset_info_st *charset;

  unsigned int  server_language;

} MYSQL;

这个结构代表返回行的一个查询的(SELECT, SHOW, DESCRIBE, EXPLAIN)的结果。返回的数据称为“数据集”，用过数据库的朋友应该对数据库中查询后得到的结果集不会陌生，在C的API里对应的就是MYSQL_RES了，从数据库读取数据，最后就是从MYSQL_RES中读取数据。

typedef struct st_mysql_res {

  my_ulonglong row_count;

  unsigned int  field_count, current_field;

  MYSQL_FIELD   *fields;

  MYSQL_DATA    *data;

  MYSQL_ROWS    *data_cursor;

  MEM_ROOT      field_alloc;

  MYSQL_ROW     row;            /* If unbuffered read */

  MYSQL_ROW     current_row;    /* buffer to current row */

  unsigned long *lengths;       /* column lengths of current row */

  MYSQL         *handle;        /* for unbuffered reads */

  my_bool       eof;            /* Used my mysql_fetch_row */

} MYSQL_RES;