Connect a C application to OceanBase Database

This topic describes how to connect a C application to OceanBase Database.

Prerequisites

Before you install OceanBase Connector/C, make sure that you have set up the basic database development environment that meets the following requirements:

• The GNU Compiler Collection (GCC) version is 3.4.6 or later. Version 4.8.5 is recommended.

• The CMake version is 2.8.12 or later.

Install OceanBase Connector/C

Install Linux

Obtain the RPM packages of OBClient and OceanBase Connector/C, which is also known as libobclient.

You need to visit the image repository and find the installation packages based on your system version. For more information, see Software and hardware requirements.

1. Install libobclient.

   sudo rpm -ivh libobclient-xx.x86_64.rpm
   

2. Install OBClient.

   sudo rpm -ivh obclient-xx.x86_64.rpm
   

   Note

   OBClient depends on libobclient. Therefore, you must install libobclient first.

Compile OBClient from source code

OceanBase Database provides the source code of the latest OBClient in its repository on Github, which also includes the repository of libobclient.

1. Install the dependency tool.

   sudo yum install -y git cmake gcc make openssl-devel ncurses-devel rpm-build  gcc-c++ bison bison-devel zlib-devel gnutls-devel libxml2-devel openssl-devel \
   libevent-devel libaio-devel
   

2. Compile and package the code.

   1. Download the source code of OBClient, which also includes sub-repositories.

      git clone --recurse-submodules https://github.com/oceanbase/obclient #Download the source code of OBClient, which also includes sub-repositories.
      cd obclient
      

   2. Compile the script of libobclient.

      cd obclient/libmariadb
      sh build.sh
      

   3. Compress the libobclient program in an RPM package.

      cd rpm
      sh libobclient-build.sh
      

   4. Compile the script of OBClient.

      cd ../..  # Return to the obclient directory
      sh build.sh
      

   5. Compress the OBClient program in an RPM package.

      cd rpm
      sh obclient-build.sh
      

3. Install libobclient and OBClient.

   cd /obclient/libmariadb/rpm
   sudo rpm -ivh libobclient-xx.x86_64.rpm
   cd ../../rpm # Access the obclient/rpm directory.
   sudo rpm -ivh obclient-xx.x86_64.rpm
   

   Note

   OBClient depends on libobclient. Therefore, you must install libobclient first.

Examples

The basic methods for an application to interact with an OBServer by using OceanBase Connector/C include:

1. Call mysql_library_init() to initialize the MySQL library.

   mysql_library_init(0, NULL, NULL);
   

2. Call mysql_init() to initialize a connection handle.

   MYSQL *mysql = mysql_init(NULL);
   

3. Call mysql_real_connect() to connect to the OBServer.

   mysql_real_connect (mysql, host_name, user_name, password,
   db_name, port_num, socket_name, CLIENT_MULTI_STATEMENTS)
   

4. Call mysql_real_query() or mysql_query() to send an SQL statement to the OBServer.

   mysql_query(mysql,"sql_statement");
   

5. Call mysql_store_result() or mysql_use_result() to process the result.

   result=mysql_store_result(mysql);
   

6. Call mysql_free_result() to release the memory.

   mysql_free_result(result);
   

7. Call mysql_close() to disconnect from the OBServer.

   mysql_close(mysql);
   

8. Call mysql_library_end() to stop using libobclient.

   mysql_library_end();
   

Sample code

The following sample code uses the mysql_test.c file as an example:

#include "mysql.h"
#include <stdio.h>
#include <stdlib.h>

int main(int argc, char** argv)
{
  mysql_library_init(0, NULL, NULL);
  MYSQL *mysql = mysql_init(NULL);
  char* host_name = "172.xx.xx.xx";//set your mysql host
  char* user_name = "r***"; //set your user_name
  char* password = "******"; //set your password
  char* db_name = "test"; //set your databasename
  int port_num = 2883; //set your mysql port
  char* socket_name = NULL;
  MYSQL_RES* result;
  int status = 0;
  /* connect to server with the CLIENT_MULTI_STATEMENTS option */
  if (mysql_real_connect (mysql, host_name, user_name, password,
    db_name, port_num, socket_name, CLIENT_MULTI_STATEMENTS) == NULL)
  {
    printf("mysql_real_connect() failed\n");
    mysql_close(mysql);
    exit(1);
  }

  /* execute multiple statements */
  status = mysql_query(mysql,
                     "DROP TABLE IF EXISTS test_table;\
                      CREATE TABLE test_table(id INT);\
                      INSERT INTO test_table VALUES(10);\
                      UPDATE test_table SET id=20 WHERE id=10;\
                      SELECT * FROM test_table;\
                      DROP TABLE test_table");
  if (status)
  {
    printf("Could not execute statement(s)");
    mysql_close(mysql);
    exit(0);
  }

 /* process each statement result */
 do {
   /* did current statement return data? */
   result = mysql_store_result(mysql);
   if (result)
   {
     /* yes; process rows and free the result set */
     //process_result_set(mysql, result);
     mysql_free_result(result);
   }
   else          /* no result set or error */
   {
     if (mysql_field_count(mysql) == 0)
     {
       printf("%lld rows affected\n",
            mysql_affected_rows(mysql));
     }
     else  /* some error occurred */
     {
       printf("Could not retrieve result set\n");
       break;
     }
  }
  /* more results? -1 = no, >0 = error, 0 = yes (keep looping) */
  if ((status = mysql_next_result(mysql)) > 0)
    printf("Could not execute statement\n");
  } while (status == 0);

  mysql_close(mysql);
}

Parameters

• hostname: the IP address for connecting to OceanBase Database, which is usually the IP address of an OBProxy.

• username: the connection account of the tenant. By default, the username of the tenant administrator is root.

• password: the password of the connection account.

• dbname: the name of the database to be connected.

• port: the port for connecting to OceanBase Database, which is also the listening port of the OBProxy. Default value: 2883, which can be customized.

After you edit the code, run the following command to compile and execute the file:

//Compile the file.
g++ -I/u01/obclient/include/ -L/u01/obclient/lib -lobclnt mysql_test.c -o mysql_test
//Specify the execution path.
export LD_LIBRARY_PATH=/u01/obclient/lib
//Run the file.
./mysql_test

Note

By default, OBClient is installed in the /u01/obclient directory.