Build a C application|V4.2.0|OceanBase Database| docs|Distributed Database

This topic describes how to build a C application with OceanBase Database and OBCI.

Applicability

This topic applies only to OceanBase Database Enterprise Edition. OceanBase Database Community Edition provides only the MySQL mode.

Prerequisites

You have set up the basic database development environment.
You have a hardware environment that meets the following requirements:
- Hardware platform: x86_64
- Operating system: Linux distribution of CentOS/Redhat 7.2
- Compiler: GCC 4.8
Contact the technical support team to obtain the RPM installation packages of OBCI and LibOBClient.

Notice

Pay attention to the following points regarding the prerequisites:

Starting from OBCI V2.0.4, the include folder in the RPM package no longer contains the oci.h and ociap.h header files. For business compilation, install the Oracle clntsh RPM package first, and then use its header files.
OceanBase Database: V2.2.76 and later (V4.0 and later are recommended to experience all the features of the current version)
OBProxy (ODP): V4.0 and later (recommended)
libobclient: V2.1.1 and later
Install the Oracle driver files oracle-instantclient. Starting from OBCI V2.0.4, you also need to install the Oracle header files.
You have installed OBCI and deployed the GCC compiler in advance.

Step 1: Obtain a database connection string

Obtain a database connection string from OceanBase deployment engineer or administrator. For example:

obclient  -h100.88.xx.xx -usys@oracle -p****** -P2881

The database connection string contains parameters required for accessing the database. Before you create an application, you can log in to the database using the database connection string to verify that the parameters are correct.

The parameters are described as follows:

-h: the IP address for connecting to OceanBase Database, which is sometimes the IP address of an ODP.
-u: the username for connecting to a tenant, in the format of username@tenant name#cluster name. The default username for the administrator in Oracle mode is sys. The cluster name is not required when you directly connect to the database, but is required when you connect to the database through an ODP.
-p: the user password.
-P: the port for connecting to OceanBase Database, which is also the listening port of the ODP.

Step 2: Install the C driver

After you obtain the RPM package, run the following command as the root user in the command-line tool to install the OBCI driver:

rpm -ivh obci-<version>.x86_64.rpm
rpm -ivh libobclient-<version>.x86_64.rpm

By default, the programs and files in the package are installed in the following paths:

The header files are installed in the /u01/obclient/include path.
The library files are installed in the /u01/obclient/lib path.

Step 3: Write an application

This topic explains how to build a C application that interacts with an OBServer node in the Oracle mode of OceanBase Database using OBCI.

Initialize the OBCI environment and the thread.

/*Initialize the OBCI program environment*/
OCIInitialize(OCI_DEFAULT, NULL, NULL, NULL, NULL)

/*Initialize the environment handle*/
OCIEnvInit(&envhp, OCI_DEFAULT, 0, 0)

Allocate necessary handles and data structures.

/*Service context handle*/
OCIHandleAlloc(envhp, (dvoid **)&svchp, OCI_HTYPE_SVCCTX, 0, 0)

/*Server handle*/
OCIHandleAlloc(envhp, (dvoid **)&srvhp, OCI_HTYPE_SERVER, 0, 0)

/*Session handle*/
OCIHandleAlloc(envhp, (dvoid **)&authp, OCI_HTYPE_SESSION, 0, 0)

/*Error handle*/
OCIHandleAlloc(envhp, (dvoid **)&errhp, OCI_HTYPE_ERROR, 0, 0)

/*Describe handle*/
OCIHandleAlloc(envhp, (dvoid **)&dschp, OCI_HTYPE_DESCRIBE, 0, 0)

Connect to the database and create a user session.

/*Set the username and password*/
 OCIAttrSet(authp, OCI_HTYPE_SESSION, (text *)strUserName,
(ub4)strlen(strUserName), OCI_ATTR_USERNAME, errhp)
 OCIAttrSet(authp, OCI_HTYPE_SESSION, (text *)strPassword,
(ub4)strlen(strPassword), OCI_ATTR_PASSWORD, errhp)

/*Set the attributes of the server environment handle*/
  OCIAttrSet((dvoid *)svchp, (ub4)OCI_HTYPE_SVCCTX,(dvoid *)srvhp, (ub4)0, OCI_ATTR_SERVER, errhp)
  OCIAttrSet(svchp, OCI_HTYPE_SVCCTX, (dvoid *)authp,0, OCI_ATTR_SESSION, errhp)

/*Create and start a user session*/
  OCISessionBegin(svchp, errhp, authp, OCI_CRED_RDBMS, OCI_DEFAULT)
  OCIHandleAlloc(envhp, (dvoid **)&stmthp, OCI_HTYPE_STMT, 0, 0)

Exchange data with OceanBase Server through SQL statements, and then process the data. The execution steps of an SQL statement in an OBCI application are as follows:

Call the OCIStmtPrepare() or OCIStmtPrepare2() function to prepare the SQL statement.

OCIStmtPrepare(stmthp, errhp, (text *)sql, strlen(sql), OCI_NTV_SYNTAX,OCI_DEFAULT)

Call the OCIBindByPos() or OCIBindByName() function to bind the addresses of input variables to the placeholders in the DML statement.

OCIBindByPos(stmthp, &bidhp[0], errhp, 1, &szpersonid,
                 sizeof(szpersonid), SQLT_INT, NULL, NULL, NULL, 0, NULL, 0)

OCIBindByName(stmthp, &bidhp[0], errhp, (const OraText*)":personid", 9, &szpersonid,
                  sizeof(szpersonid), SQLT_INT, NULL, NULL, NULL, 0, NULL, 0)

Call the OCIStmrExecute() function to execute the SQL statement.

OCIStmtExecute(svchp, stmthp, errhp, (ub4)1, (ub4)0, (CONST OCISnapshot *)0, 
(OCISnapshot *)0, (ub4)OCI_DEFAULT)

Call the OCIDefineByPos() function to define output variables for the output items in the SQL statement.

OCIDefineByPos(stmthp, &defhp[0], errhp, 1, &szpersonid,
sizeof(szpersonid), SQLT_INT, &ind[0], 0, 0, OCI_DEFAULT)

Call the OCIStmtFetch() function to retrieve the result set of a query.
```
OCIStmtFetch(stmthp, errhp, 1, OCI_FETCH_NEXT, OCI_DEFAULT)
```

End the user session and disconnect from the database.

/*End the session*/
  OCISessionEnd(svchp, errhp, authp, (ub4)0)

/*Disconnect from the database*/
  OCIServerDetach(srvhp, errhp, OCI_DEFAULT)

Release the handles allocated in the program.

OCIHandleFree((dvoid *)dschp, OCI_HTYPE_DESCRIBE)
OCIHandleFree((dvoid *)stmthp, OCI_HTYPE_STMT)
OCIHandleFree((dvoid *)errhp, OCI_HTYPE_ERROR)
OCIHandleFree((dvoid *)authp, OCI_HTYPE_SESSION)
OCIHandleFree((dvoid *)svchp, OCI_HTYPE_SVCCTX)
OCIHandleFree((dvoid *)srvhp, OCI_HTYPE_SERVER)

Sample code

The content of the test.c file is as follows:

/**********************************************************
* Copyright(C) 2014 - 2020 Alibaba Inc. All Rights Reserved.
*
*  Filename: ob_oci_test.c
*  Description: ----
*  Create: 2020-07-07 10:14:59
*  Last Modified: 2020-07-07 10:14:59
***********************************************************/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <malloc.h>
#include "oci.h"
/* Declare handles */
OCIEnv *envhp;       /* Environment handle */
OCISvcCtx *svchp;    /* Service environment handle */
OCIServer *srvhp;    /* Server handle */
OCISession *authp;   /* Session handle */
OCIStmt *stmthp;     /* Statement handle */
OCIDescribe *dschp;  /* Describe handle */
OCIError *errhp;     /* Error handle */
OCIDefine *defhp[3]; /* Define handle */
OCIBind *bidhp[4];   /* Bind handle */
sb2 ind[3];          /* Indicator variables */
/* Bind parameters in the result set of the select statement */
int szpersonid; /* Stores the personid column */
text szname[51];    /* Stores the name column */
text szemail[51];   /* Stores the mail column */
char sql[256];      /* Stores the executed SQL statement */

int main(int argc, char *argv[])
{
  char strServerName[50];
  char strUserName[50];
  char strPassword[50];
  /* Set the server name, username, and password */
  strcpy(strServerName, "172.30.xx.xx:2881");
  strcpy(strUserName, "s**@oracle");
  strcpy(strPassword, "******");
  /* Initialize the OCI application environment */
  OCIInitialize(OCI_DEFAULT, NULL, NULL, NULL, NULL);
  /* Initialize the environment handle */
  OCIEnvInit(&envhp, OCI_DEFAULT, 0, 0);
  /* Allocate handles */
  OCIHandleAlloc(envhp, (dvoid **)&svchp, OCI_HTYPE_SVCCTX, 0, 0);
  /* Service environment handle */
  OCIHandleAlloc(envhp, (dvoid **)&srvhp, OCI_HTYPE_SERVER, 0, 0);
  /* Server handle */
  OCIHandleAlloc(envhp, (dvoid **)&authp, OCI_HTYPE_SESSION, 0, 0);
  /* Session handle */
  OCIHandleAlloc(envhp, (dvoid **)&errhp, OCI_HTYPE_ERROR, 0, 0);
  /* Error handle */
  OCIHandleAlloc(envhp, (dvoid **)&dschp, OCI_HTYPE_DESCRIBE, 0, 0);
  /* Describe handle */
  /* Connect to the server */
  OCIServerAttach(srvhp, errhp, (text *)strServerName, (sb4)strlen(strServerName), OCI_DEFAULT);
  /* Set the username and password */
  OCIAttrSet(authp, OCI_HTYPE_SESSION, (text *)strUserName, (ub4)strlen(strUserName), OCI_ATTR_USERNAME, errhp);
  OCIAttrSet(authp, OCI_HTYPE_SESSION, (text *)strPassword, (ub4)strlen(strPassword), OCI_ATTR_PASSWORD, errhp);
  /* Set the attributes of the server environment handle */
  OCIAttrSet((dvoid *)svchp, (ub4)OCI_HTYPE_SVCCTX, (dvoid *)srvhp, (ub4)0, OCI_ATTR_SERVER, errhp);
  OCIAttrSet(svchp, OCI_HTYPE_SVCCTX, (dvoid *)authp, 0, OCI_ATTR_SESSION, errhp);
  /* Create and start a user session */
  OCISessionBegin(svchp, errhp, authp, OCI_CRED_RDBMS, OCI_DEFAULT);
  OCIHandleAlloc(envhp, (dvoid **)&stmthp, OCI_HTYPE_STMT, 0, 0);
  /* Statement handle */

  /************************************************************************/
  /* Create a table named person. */
  /************************************************************************/
  static text* SQL_CREATE_TB = (text*)"create table person(personid number, name varchar(256), email  varchar(256))";
  /* Prepare an SQL statement */
  OCIStmtPrepare(stmthp, errhp, SQL_CREATE_TB, strlen((char *)SQL_CREATE_TB),OCI_NTV_SYNTAX, OCI_DEFAULT);
  /* Execute the SQL statement */
  OCIStmtExecute(svchp, stmthp, errhp, 1, 0, 0, 0, OCI_DEFAULT);
  /* Commit to the database */
  OCITransCommit(svchp, errhp, OCI_DEFAULT);

  /************************************************************************/
  /* Insert data. */
  /************************************************************************/
  memset(sql, 0, sizeof(sql));
  strcpy(sql, "insert into person values(:personid,:name,:email)");
  /* Prepare an SQL statement */
  OCIStmtPrepare(stmthp, errhp, (text *)sql, strlen(sql),OCI_NTV_SYNTAX, OCI_DEFAULT);
  /* Bind the input columns */
  OCIBindByName(stmthp, &bidhp[0], errhp, (const OraText*)":personid", 9, &szpersonid, sizeof(szpersonid), SQLT_INT, NULL, NULL, NULL, 0, NULL, 0);
  OCIBindByName(stmthp, &bidhp[2], errhp, (const OraText*)":name", 5, szname, sizeof(szname), SQLT_STR, NULL, NULL, NULL, 0, NULL, 0);
  OCIBindByName(stmthp, &bidhp[3], errhp, (const OraText*)":email", 6, szemail, sizeof(szemail), SQLT_STR, NULL, NULL, NULL, 0, NULL, 0);
  /* Set the input parameters */
  szpersonid = 1;
  memset(szname, 0, sizeof(szname));
  strcpy((char*)szname, "obtest");
  memset(szemail, 0, sizeof(szemail));
  strcpy((char*)szemail, "t***@ob.com");
  /* Execute the SQL statement */
  OCIStmtExecute(svchp, stmthp, errhp, (ub4)1, (ub4)0, (CONST OCISnapshot *)0, (OCISnapshot *)0, (ub4)OCI_DEFAULT);
  /* Commit to the database */
  OCITransCommit(svchp, errhp, OCI_DEFAULT);

  /************************************************************************/
  /* Query the person table. */
  /************************************************************************/
  strcpy(sql, "select personid ,name,email from person;");
  /* Prepare an SQL statement */
  OCIStmtPrepare(stmthp, errhp, (text *)sql, strlen(sql), OCI_NTV_SYNTAX, OCI_DEFAULT);
  /* Bind the output columns */
  OCIDefineByPos(stmthp, &defhp[0], errhp, 1, &szpersonid, sizeof(szpersonid), SQLT_STR, &ind[0], 0, 0, OCI_DEFAULT);
  OCIDefineByPos(stmthp, &defhp[1], errhp, 2, (ub1 *)szname, sizeof(szname), SQLT_STR, &ind[1], 0, 0, OCI_DEFAULT);
  OCIDefineByPos(stmthp, &defhp[2], errhp, 3, (ub1 *)szemail, sizeof(szemail), SQLT_STR, &ind[2], 0, 0, OCI_DEFAULT);
  /* Execute the SQL statement */
  OCIStmtExecute(svchp, stmthp, errhp, (ub4)0, 0, NULL, NULL,
                 OCI_DEFAULT);
  printf("%-10s%-10s%-10s\n", "PERSONID", "NAME", "email");
  while ((OCIStmtFetch(stmthp, errhp, 1, OCI_FETCH_NEXT, OCI_DEFAULT)) != OCI_NO_DATA)
  {
    printf("%-10d", szpersonid);
    printf("%-10s", szname);
    printf("%-10s\n", szemail);
    break;
  }
  /* Commit to the database */
  OCITransCommit(svchp, errhp, OCI_DEFAULT);

  /************************************************************************/
  /* Drop the person table. */
  /************************************************************************/
  static text* SQL_DROP_TB   = (text*)"drop table person";
  /* Prepare an SQL statement */
  OCIStmtPrepare(stmthp, errhp, (text*)SQL_DROP_TB, strlen((char *)SQL_DROP_TB), OCI_NTV_SYNTAX, OCI_DEFAULT);
  /* Execute the SQL statement */
  OCIStmtExecute(svchp, stmthp, errhp, 1, 0, 0, 0, OCI_COMMIT_ON_SUCCESS);
  /* Commit to the database */
  OCITransCommit(svchp, errhp, OCI_DEFAULT);

  // End the session.
  OCISessionEnd(svchp, errhp, authp, (ub4)0);
  // Disconnect from the database.
  OCIServerDetach(srvhp, errhp, OCI_DEFAULT);
  // Free the OCI handles.
  OCIHandleFree((dvoid *)dschp, OCI_HTYPE_DESCRIBE);
  OCIHandleFree((dvoid *)stmthp, OCI_HTYPE_STMT);
  OCIHandleFree((dvoid *)errhp, OCI_HTYPE_ERROR);
  OCIHandleFree((dvoid *)authp, OCI_HTYPE_SESSION);
  OCIHandleFree((dvoid *)svchp, OCI_HTYPE_SVCCTX);
  OCIHandleFree((dvoid *)srvhp, OCI_HTYPE_SERVER);
  return 0;
}

Modify the database connection parameters in the code. Values of the parameters are from the database connection string obtained in Step 1.

strcpy(strServerName, "172.30.xx.xx:2881");
strcpy(strUserName, "s**@oracle");
strcpy(strPassword, "******");

strServerName: the IP address and port number for connecting to OceanBase Database, which is usually the IP address of an ODP and the port number for accessing it. The value of this parameter is in the IP:port format.
strUserName: the username for connecting to a tenant, in the format of username@tenant name#cluster name. The default value for the username of the administrator in Oracle mode is sys. The cluster name is not required when you directly connect to the database, but is required when you connect to the database through an ODP.
strPassword: the user password.

Step 4: Run the application

After you edit the code, run the following command:

// Compile
gcc test.c -I/u01/obclient/include /u01/obclient/lib/libobci.a -L/usr/local/lib64 -lstdc++ -lpthread -ldl -lm -g -o test

If the execution result shown in the following figure is returned after the compilation, the database is connected and the statement is executed successfully.

./test

PERSONID  NAME      email
1         obtest    t***@ob.com

More information

For more information about OBCI, see the OceanBase C API chapter on the official website.

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