Connect a C application to OceanBase Database|V3.1.4|OceanBase Database| docs|Distributed Database

This topic provides a code example on how to connect a C application to OceanBase Database.

Prerequisites

Before installing and using OceanBase Connector/C, make sure you have set up a basic database development environment. The requirements are as follows:

The GCC version is 3.4.6 or later (recommended version: 4.8.5).
The CMake version is 2.8.12 or later.

Install the C driver

Install Linux

Download the OceanBase Connector/C installation package (libobclient) and the obclient installation package.

Operating System	Installation Package Download Address
Anolis 7, CentOS 7, RedHat 7, Ubuntu 20.X, Debian 9.X	el7 download address (Simplified Chinese)
Anolis 8, CentOS 8, RedHat 8, Debian 10	el8 download address (Simplified Chinese)

Note: It is recommended that you download the latest version of the installation package.

Install libobclient.

Note: Since obclient depends on libobclient, you need to install libobclient first.
```
sudo rpm -ivh libobclient-xx.x86_64.rpm
```
Install obclient.
```
sudo rpm -ivh obclient-xx.x86_64.rpm
```

Compile from source code

OceanBase's GitHub repository provides the source code for the latest development version of obclient (including libobclient).

Install dependencies.

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

Code compilation and packaging

Download the obclient source code (including libobclient).

git clone --recurse-submodules https://github.com/oceanbase/obclient #Download obclient source code, including libobclient
cd obclient

Complie the libobclient code.
```
cd obclient/libmariadb
sh build.sh
```
Package the RPM installation packages for libobclient.
```
cd rpm
sh libobclient-build.sh
```

Complie the obclient code.

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

Package the RPM installation packages for obclient.
```
cd rpm
sh obclient-build.sh
```

Install libobclient and obclient.

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

Note: Since obclient depends on libobclient, you need to install libobclient first.

Operation example

To connect a C application to OceanBase Database through OceanBase Connector/C, perform the following steps:

Call mysql_library_init() to initialize the MySQL library.
```
mysql_library_init(0, NULL, NULL);
```
Call mysql_init() to initialize a connection handle.
```
MYSQL *mysql = mysql_init(NULL);
```

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)

Call mysql_real_query() or mysql_query() to send an SQL statement to the OBServer.
```
mysql_query(mysql,"sql_statement");
```
Call mysql_store_result() or mysql_use_result() to process its results.
```
result=mysql_store_result(mysql);
```
Call mysql_free_result() to release the memory.
```
mysql_free_result(result);
```
Call mysql_close() to close the connection to the OBServer.
```
mysql_close(mysql);
```
Call mysql_library_end() to end the use of libobclient.
```
mysql_library_end();
```

Sample code

The mysql_test.c file is used as an example, with the following code:

#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 = "***1**"; //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);
}

Parameter description

hostname: IP address to connect to OceanBase Database, usually the OBProxy address.
port: Port to connect to OceanBase Database, also the listening port of OBProxy. The default port is 2883, which can be customized.
dbname: Name of the database to be accessed.
username: The tenant's connection account, and the tenant's administrator username is root by default.
password: Account password.

After the code is edited, it can be compiled and executed with the following commands:

//Compile the code
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
//Execute the code
./ mysql_test

Note: The default path for obclient installation is /u01/obclient.

Community Edition

Connect a C application to OceanBase Database