MySQL Learning note _12_linux under C++/C connection MySQL database (ii)--SQL to return data

 Linuxunderc++/cConnectionMySQLDatabase(two)--returns the dataSQLCited:

returns the data SQL a data record that satisfies a condition is fetched from the database by a query statement

from MySQL Database Value Oh function Retrieve data Yes 4 a step:

1 ) issue a query

2 ) Retrieve data

3 ) processing Data

4 ) to collate the required data

with mysql_query () issue a query that retrieves data that can be used Mysql_store_result () or Mysql_use_result () , depending on how the data is retrieved, and then the call mysql_fetch_row () to process the data, and finally, you must call the mysql_free_result () to allow MySQL perform the necessary finishing work.

1, extract all data at once [CPP]View Plaincopyprint?

2. Mysql_res *mysql_store_result (MySQL * connection);
4. //successfully returned struct pointer, failed to return null   
6. My_ulonglong Mysql_num_row (Mysql_res * result);
8. //Decelerate The actual number of rows returned   
10. Mysql_row mysql_fetch_row (Mysql_res * result);
12. //The struct that gets the result from Mysql_store_result () and retrieves a single row from it, returning NULL when there is no more data, or when there is an error   
14. void  mysql_free_result (Mysql_res * result);
16. //Make the MySQL database tidy up the allocated objects and close the connection.   

Mysql_res *mysql_store_result (MySQL * connection);//successful return of struct pointer, failed to return Nullmy_ulonglong mysql_num_row (mysql_res * result) ;//decelerate the number of rows actually returned Mysql_row mysql_fetch_row (mysql_res * result),//The structure from Mysql_store_result (), and retrieve a single row from it, when no more data is available, or error, return nullvoid mysql_free_result (mysql_res * result);//make the MySQL database tidy up the allocated objects and close the connection.

Example:

[CPP]View Plaincopyprint?

2. #include <iostream>   
4. #include <fstream>   
6. #include <cstdlib>   
8. #include <mysql/mysql.h>   
10. using   namespace std;
14. void  mysql_err_function (MySQL * connection);
18. int Main ()
20. {
22. MYSQL * Connection;
24. Connection = Mysql_init (NULL);
28. if (!connection)
30. {
32. Mysql_err_function (connection);
34. }
38. Connection = Mysql_real_connect (connection,"localhost","root","123456"   ,"test", 0,null,0);
42. if (!connection)
44. {
46. Mysql_err_function (connection);
48. }
52. cout << "Connection to MySQL Server is Success ..." << Endl;
54. string query;
56. Getline (Cin,query);
60. int  res = mysql_query (Connection,query.c_str ());
62. if (RES)
64. {
66. Mysql_err_function (connection);
68. }
72. Mysql_res * my_res = Mysql_store_result (connection);
76. cout << "Retrieved" << mysql_num_rows (my_res) << "Rows" << Endl  ;
80. Mysql_row Sqlrow;
82. while ((Sqlrow = Mysql_fetch_row (my_res)))
84. {
86. cout << "fetched data ..." << Endl;
88. }
90. Mysql_free_result (My_res);
94. Mysql_close (connection);
96. cout << "Connection to MySQL Server is closed!"  << Endl;
100. return  0;
102. }
106. void mysql_err_function (MySQL * connection)
108. {
110. if (Mysql_errno (connection))
112. {
114. cout << "Error" << Mysql_errno (connection) << ":"
116. << mysql_error (connection) << Endl;
120. Exit (-1);
122. }
124. }

#include <iostream> #include <fstream> #include <cstdlib> #include <mysql/mysql.h>using namespace Std;void mysql_err_function (MySQL * connection); int main () {MySQL * connection;connection = mysql_init (NULL);    if (!connection) {mysql_err_function (connection);} Connection = Mysql_real_connect (connection, "localhost", "root", "123456", "Test", 0,null,0); if (!connection) {Mysql_ Err_function (connection);} cout << "Connection to MySQL Server is Success ..." << endl;string query;getline (cin,query); int res = Mysql_que    Ry (Connection,query.c_str ()); if (res) {mysql_err_function (connection);} Mysql_res * my_res = Mysql_store_result (connection), cout << "Retrieved" << mysql_num_rows (my_res) << " Rows "<< Endl; Mysql_row sqlrow;while ((Sqlrow = Mysql_fetch_row (my_res))) {cout << "fetched data ..." << Endl;} Mysql_free_result (my_res); mysql_close (connection); cout << "connection to MySQL Server is closed!" << Endl; return 0;} void Mysql_Err_function (MYSQL * connection) {if (Mysql_errno (connection)) {cout << "Error" << Mysql_errno (Connection) & lt;< ":" << mysql_error (Connection) << Endl;exit (-1);}}

2, fetching one row of data at a time for processing a large number of data sets [CPP]View Plaincopyprint?

1. Mysql_res *mysql_use_result (MySQL * connection);
2. //Successfully returned result set, failed to return null   

Mysql_res *mysql_use_result (MySQL * connection);  

Taking all the data at once increases the network load and increases the latency, but it can guarantee the integrity of the data.

Example:

[CPP]View Plaincopyprint?

2. #include <iostream>   
4. #include <cstdlib>   
6. #include <mysql/mysql.h>   
8. using   namespace std;
12. void  mysql_err_function (MySQL * connection);
16. int Main ()
18. {
20. MYSQL * Connection;
22. Connection = Mysql_init (NULL);
26. if (Mysql_real_connect (connection,"localhost","root"," 123456 "," test ", 0,null,0))
28. {
30. cout << "Connection to MySQL Server is succeed ..." << Endl;
32. string query;
34. Getline (Cin,query);
38. int  res = mysql_query (Connection,query.c_str ());
40. if (RES)
42. {
44. Mysql_err_function (connection); //mysql_err_function () Implementation code reference above example   
46. }
48. Else   
50. {
52. Mysql_res * my_res = Mysql_use_result (connection);
54. if (my_res)
56. {
58. Mysql_row Sqlrow;
60. while ((Sqlrow = Mysql_fetch_row (my_res)))
62. {
64. cout << "fetching the Data ..." << Endl;
66. }
70. Mysql_free_result (My_res);
72. }
74. Else   
76. {
78. Mysql_err_function (connection);
80. }
82. }
86. Mysql_close (connection);
88. cout << "Connection to MySQL Server is closed!"  << Endl;
90. }
92. Else   
94. {
96. Mysql_err_function (connection);
98. }
100. }

MySQL Learning note _12_linux under C++/C connection MySQL database (ii)--SQL to return data