Application of Double links in connection between MySQL and C

// C write the data structure used by the MySQL Connection Program <br/> struct harvis_mysql_struct {<br/> MySQL * conn; // The MySQL connection established, global variable <br/> int ID; // sequence number connecting to MySQL, starting from 0 and starting from-1 <br/> unsigned int query_times; // The number of queries executed on a MySQL connection. The initial value is 0 <br/> struct harvis_mysql_struct * Next, * Prev; // point to the next struct <br/> }; <br/> // Max harvis_mysql number <br/> # define maxskillmysql 16 // currently supports establishing 16 dB connections with MySQL at the same time <br/> static struct harvis_mysql_struct * harvis_mysql_entry [m Axskillmysql]; // A array of struct harvis_mysql_struct typed pointer <br/> static struct harvis_mysql_struct limit [maxskillmysql]; <br/> static struct harvis_mysql_struct * Limit = NULL; // unused struct harvis_mysql_struct Single-Chain header pointer <br/> static struct harvis_mysql_struct * harvis_mysql_using_head = NULL; // use the struct harvis_mysql_struct Single-Chain header pointer <br/> static int harvis_mysql_entry _ Id =-1; // serial number. Each time an entry is used, it is incremented by 1. Every time an entry is abandoned, it is subtracted by 1. <br/>/* <br/> * init_harvis_mysql_list-concatenates elements in the array into a linked list. <br/> * void: <br/> */<br/> void init_harvis_mysql_list (void) <br/>{< br/> int I; <br/> for (I = 0; I <maxskillmysql; I ++) <br/> harvis_mysql_entry [I] = & harvis_mysql_entry2 [I]; <br/> for (I = 0; I <maxskillmysql-1; I ++) {// one's next point the next one <br/> harvis_mysql_entry [I]-> next = Harvis _ Mysql_entry [I + 1]; <br/> harvis_mysql_entry [I]-> conn = NULL; <br/> harvis_mysql_entry [I]-> id =-1; <br/> harvis_mysql_entry [I]-> query_times = 0; <br/>}< br/> // initialize the last element of the array <br/> harvis_mysql_entry [I]-> next = NULL; // last element's next pointer <br/> harvis_mysql_entry [I]-> conn = NULL; <br/> harvis_mysql_entry [I]-> id =-1; <br/> harvis_mysql_entry [I]-> query_times = 0; <br/> // initializes the front pointer. <br/> For (I = 1; I <maxskillmysql; I ++) <br/> harvis_mysql_entry [I]-> Prev = harvis_mysql_entry [I-1]; <br/> harvis_mysql_entry [0]-> Prev = NULL; <br/> // assign a value to the header pointer of the idle list. <Br/> harvis_mysql_free_head = harvis_mysql_entry [0]; // free point to the first element of the List <br/>}< br/> // get a struct harvis_mysql_struct type element from the header <br/> struct harvis_mysql_struct * get_harvis_mysql_entry () <br/>{ <br/> struct harvis_mysql_struct * entry; <br/> // checks whether there are idle entries. <br/> If (harvis_mysql_free_head = NULL) <br/> return (struct harvis_mysql_struct *) 0; // if no entry is available, a null pointer is returned. <br/> entry = Harvis_mysql_free_head; <br/> harvis_mysql_free_head = harvis_mysql_free_head-> next; // move free_head to the next entry <br/> If (harvis_mysql_free_head! = NULL) <br/> harvis_mysql_free_head-> Prev = NULL; // The pre-pointer value is null <br/> // entry-> next = NULL; <br/> // Add the entry to the used list <br/> If (harvis_mysql_using_head = NULL) {<br/> entry-> next = NULL; <br/> harvis_mysql_using_head = entry; <br/> harvis_mysql_using_head-> Prev = NULL; // The pre-pointer value is null <br/>} else {<br/> entry-> next = harvis_mysql_using_head; <br/> harvis_mysql_using_head = entry; <br/> harvis_mysql _ Using_head-> Prev = NULL; // The pre-pointer value is null <br/>}< br/> harvis_mysql_entry_id ++; <br/> entry-> conn = NULL; <br/> entry-> id = harvis_mysql_entry_id; <br/> entry-> query_times = 0; <br/> return (entry ); <br/>}< br/> // search by serial number from the applying linked list <br/> struct harvis_mysql_struct * search_harvis_mysql (int id) <br/> {<br/> struct harvis_mysql_struct * entry; <br/> If (ID <0 | ID> maxskillmysql-1) <br/> return (struct H Arvis_mysql_struct *) 0; // the sequence number is invalid <br/> If (harvis_mysql_using_head = NULL) <br/> return (struct harvis_mysql_struct *) 0; // The linked list being applied is empty. <br/> for (Entry = harvis_mysql_using_head; entry! = NULL; entry = entry-> next) {<br/> If (Entry-> id = ID) <br/> return entry; // if no pointer is found, return the pointer of this struct <br/>}< br/> return (struct harvis_mysql_struct *) 0; // No found, returns a null pointer <br/>}< br/> // put a struct harvis_mysql_struct element (cleared) to the header of the List <br/> void free_harvis_mysql_entry (int I) <br/>{< br/> struct harvis_mysql_struct * entry; <br/> entry = search_harvis_mysql (I); <br/> If (entry! = NULL) {<br/> If (Entry-> next! = NULL & Entry-> Prev! = NULL) {<br/> entry-> Prev-> next = entry-> next; // perform the unlink operation <br/> entry-> next-> Prev = entry-> Prev; // remove <br/>} else {<br/> harvis_mysql_using_head = NULL; <br/>}< br/> harvis_mysql_entry_id --; <br/> // clear the entry for future use <br/> entry-> conn = NULL; <br/> entry-> id =-1; <br/> entry-> query_times = 0; <br/> entry-> next = harvis_mysql_free_head; // Add to the header of the idle Object List <br/> entry-> Prev = NULL; // The value of the pre-pointer is null. <Br/> harvis_mysql_free_head = entry; </P> <p >}< br/> // Add an element to the list header <br/> // struct harvis_mysql_struct * add_harvis_mysql_entry (struct harvis_mysql_struct * head, struct harvis_mysql_struct * entry) <br/> // {</P> <p> //} <br/> // obtain the tail element of the list. <br/> struct harvis_mysql_struct * get_harvis_mysql_tail (struct harvis_mysql_struct * head) <br/>{< br/> struct harvis_mysql_struct * entry; <br/> for (Entry = head; Entry-> next! = NULL; entry = entry-> next) <br/>; // empty statement, cannot be omitted <br/> return (entry ); <br/>}< br/> int harvis_mysql_length (struct harvis_mysql_struct * head) <br/>{< br/> int counter = 0; <br/> struct harvis_mysql_struct * entry; <br/> for (Entry = head; entry! = NULL; entry = entry-> next) <br/> counter ++; <br/> return counter; <br/>}