2 OCI Programming Basics

Allocating and Freeing Handles

Your application allocates all handles (except the bind, define, and thread handles) with respect to a particular environment handle. You pass the environment handle as one of the parameters to the handle allocation call. The allocated handle is then specific to that particular environment.

The bind and define handles are allocated with respect to a statement handle, and contain information about the statement represented by that handle.

The environment handle is allocated and initialized with a call to OCIEnvCreate() or to OCIEnvNlsCreate(), one of which is required by all OCI applications.

All user-allocated handles are initialized using the OCI handle allocation call, OCIHandleAlloc().

Here are the various types of handles: session handle, direct path context handle, thread handle, COR handle, subscription handle, describe handle, statement handle, service context handle, error handle, server handle, connection pool handle, event handle, and administration handle.

The thread handle is allocated with the OCIThreadHndInit() call.

An application must free all handles when they are no longer needed. The OCIHandleFree() function frees all handles.

Handles lessen the need for global variables. Handles also make error reporting easier. An error handle is used to return errors and diagnostic information.

Environment Handle

The environment handle defines a context in which all OCI functions are invoked. Each environment handle contains a memory cache, which enables fast memory access. All memory allocation under the environment handle is done from this cache. Access to the cache is serialized if multiple threads try to allocate memory under the same environment handle. When multiple threads share a single environment handle, they may block on access to the cache.

The environment handle is passed as the parent parameter to the OCIHandleAlloc() call to allocate all other handle types. Bind and define handles are allocated implicitly.

Error Handle

The error handle is passed as a parameter to most OCI calls. The error handle maintains information about errors that occur during an OCI operation. If an error occurs in a call, the error handle can be passed to OCIErrorGet() to obtain additional information about the error that occurred.

Allocating the error handle is one of the first steps in an OCI application because most OCI calls require an error handle as one of its parameters.

Service Context and Associated Handles

A service context handle defines attributes that determine the operational context for OCI calls to a server. The service context contains three handles as its attributes, that represent a server connection, a user session, and a transaction. These attributes are illustrated in Figure 2-2, "Components of a Service Context":

Figure 2-2 Components of a Service Context

Description of "Figure 2-2 Components of a Service Context"

• A server handle identifies a connection to a database. It translates into a physical connection in a connection-oriented transport mechanism.

• A user session handle defines a user's roles and privileges (also known as the user's security domain), and the operational context in which the calls execute.

• A transaction handle defines the transaction in which the SQL operations are performed. The transaction context includes user session state information, including any fetch state and package instantiation.

Breaking the service context down in this way provides scalability and enables programmers to create sophisticated multitiered applications and transaction processing (TP) monitors for execute requests on behalf of multiple users on multiple application servers and different transaction contexts.

You must allocate and initialize the service context handle with OCIHandleAlloc() or OCILogon() before you can use it. The service context handle is allocated explicitly by OCIHandleAlloc(). It can be initialized using OCIAttrSet() with the server, session, and transaction handle. If the service context handle is allocated implicitly using OCILogon(), it is already initialized.

Applications maintaining only a single user session for each database connection at any time can call OCILogon() to get an initialized service context handle.

In applications requiring more complex session management, the service context must be explicitly allocated, and the server and user session handles must be explicitly set into the service context. OCIServerAttach() and OCISessionBegin() calls initialize the server and user session handle respectively.

An application will only define a transaction explicitly if it is a global transaction or there are multiple transactions active for sessions. It will be able to work correctly with the implicit transaction created automatically by OCI when the application makes changes to the database.

Statement, Bind, and Define Handles

A statement handle is the context that identifies a SQL or PL/SQL statement and its associated attributes. This is shown in Figure 2-3, "Statement Handles".

Figure 2-3 Statement Handles

Description of "Figure 2-3 Statement Handles"

Information about input and output bind variables is stored in bind handles. The OCI library allocates a bind handle for each placeholder bound with the OCIBindByName() or OCIBindByPos() function. The user must not allocate bind handles. They are implicitly allocated by the bind call.

Fetched data returned by a query (select statement) is converted and retrieved according to the specifications of the define handles. The OCI library allocates a define handle for each output variable defined with OCIDefineByPos(). The user must not allocate define handles. They are implicitly allocated by the define call.

Bind and define handles are implicitly allocated by the OCI library, and are transparently reused if the bind or define operation is repeated. The actual value of the bind or define handle is needed by the application for advanced bind or define operations described in the chapter on binding and defining. The handles are freed when the statement hand is freed or when a new statement is prepared on the statement handle. Explicitly allocating bind or define handles may lead to memory leaks. Expliticly freeing bind of define handles may cause abnormal program termination.

Describe Handle

The describe handle is used by the OCI describe call, OCIDescribeAny(). This call obtains information about schema objects in a database (for example, functions, procedures). The call takes a describe handle as one of its parameters, along with information about the object being described. When the call completes, the describe handle is populated with information about the object. The OCI application can then obtain describe information through the attributes of parameter descriptors.

Complex Object Retrieval Handle

The complex object retrieval (COR) handle is used by some OCI applications that work with objects in an Oracle database server. This handle contains COR descriptors, which provide instructions for retrieving objects referenced by another object.

Thread Handle

For information about the thread handle, which is used in multithreaded applications:

Subscription Handle

The subscription handle is used by an OCI client application that registers and subscribes to receive notifications of database events or events in the AQ namespace. The subscription handle encapsulates all information related to a registration from a client.

Direct Path Handles

The direct path handles are necessary for an OCI application that uses the direct path load engine in the Oracle database server. The direct path load interface enables the application to access the direct block formatter of the Oracle server. Figure 2-4, "Direct Path Handles" shows the different kinds of direct path handles.

Figure 2-4 Direct Path Handles

Description of "Figure 2-4 Direct Path Handles"

Connection Pool Handle

The connection pool handle is used for applications that pool physical connections into virtual connections by calling specific OCI functions.

Handle Attributes

All OCI handles have attributes that represent data stored in that handle. You can read handle attributes using the attribute get call, OCIAttrGet(), and you can change them with the attribute set call, OCIAttrSet().

For example, the following statements set the user name in the session handle by writing to the OCI_ATTR_USERNAME attribute:

text username[] = "hr";
err = OCIAttrSet ((void *) mysessp, OCI_HTYPE_SESSION, (void *)username,
      (ub4) strlen((char *)username), OCI_ATTR_USERNAME, (OCIError *) myerrhp);

Some OCI functions require that particular handle attributes be set before the function is called. For example, when OCISessionBegin() is called to establish a user's login session, the user name and password must be set in the user session handle before the call is made.

Other OCI functions provide useful return data in handle attributes after the function completes. For example, when OCIStmtExecute() is called to execute a SQL query, describe information relating to the select-list items is returned in the statement handle.

ub4 parmcnt;
/* get the number of columns in the select list */
err = OCIAttrGet ((void  *)stmhp, (ub4)OCI_HTYPE_STMT, (void  *)
         &parmcnt, (ub4 *) 0, (ub4)OCI_ATTR_PARAM_COUNT, errhp);

Snapshot Descriptor

The snapshot descriptor is an optional parameter to the execute call, OCIStmtExecute(). It indicates that a query is being executed against a particular database snapshot which represents the state of a database at a particular point in time.

Allocate a snapshot descriptor with a call to OCIDescriptorAlloc(), by passing OCI_DTYPE_SNAP as the type parameter.

LOB and BFILE Locators

A large object (LOB) is an Oracle datatype that can hold binary (BLOB) or character (CLOB) data. In the database, an opaque data structure called a LOB locator is stored in a LOB column of a database row, or in the place of a LOB attribute of an object. The locator serves as a pointer to the actual LOB value, which is stored in a separate location.

The OCI LOB locator is used to perform OCI operations against a LOB (BLOB or CLOB) or FILE (BFILE). OCILobXXX functions take a LOB locator parameter instead of the LOB value. OCI LOB functions do not use actual LOB data as parameters. They use the LOB locators as parameters and operate on the LOB data referenced by them.

The LOB locator is allocated with a call to OCIDescriptorAlloc(), by passing OCI_DTYPE_LOB as the type parameter for BLOBs or CLOBs, and OCI_DTYPE_FILE for BFILEs.

An OCI application can retrieve a LOB locator from the server by issuing a SQL statement containing a LOB column or attribute as an element in the select list. In this case, the application would first allocate the LOB locator and then use it to define an output variable. Similarly, a LOB locator can be used as part of a bind operation to create an association between a LOB and a placeholder in a SQL statement.

Parameter Descriptor

OCI applications use parameter descriptors to obtain information about select-list columns or schema objects. This information is obtained through a describe operation.

The parameter descriptor is the only descriptor type that is not allocated using OCIDescriptorAlloc(). You can obtain it only as an attribute of a describe handle, statement handle, or through a complex object retrieval handle by specifying the position of the parameter using an OCIParamGet() call.

ROWID Descriptor

The ROWID descriptor, OCIRowid, is used by applications that need to retrieve and use Oracle ROWIDs. To work with a ROWID using OCI release 8 or later, an application can define a ROWID descriptor for a rowid position in a SQL select-list, and retrieve a ROWID into the descriptor. This same descriptor can later be bound to an input variable in an INSERT statement or WHERE clause.

ROWIDs are also redirected into descriptors using OCIAttrGet() on the statement handle following an execute.

Date, Datetime, and Interval Descriptors

These descriptors are used by applications which use the date, datetime, or interval datatypes (OCIDate, OCIDateTime, and OCIInterval). These descriptors can be used for binding and defining, and are passed as parameters to the functions OCIDescAlloc() and OCIDescFree() to allocate and free memory.

Complex Object Descriptor

Application performance when dealing with objects may be increased through the use of complex object retrieval (COR).

Advanced Queuing Descriptors

Oracle AQ provides message queuing as an integrated part of the Oracle server.

User Memory Allocation

The OCIDescriptorAlloc() call has an xtramem_sz parameter in its parameter list. This parameter is used to specify an amount of user memory which should be allocated along with a descriptor or locator.

Typically, an application uses this parameter to allocate an application-defined structure that has the same lifetime as the descriptor or locator. This structure maybe used for application bookkeeping or storing context information.

Using the xtramem_sz parameter means that the application does not need to explicitly allocate and deallocate memory as each descriptor or locator is allocated and deallocated. The memory is allocated along with the descriptor or locator, and freeing the descriptor or locator (with OCIDescriptorFree()) frees the user's data structures as well.

The OCIHandleAlloc() call has a similar parameter for allocating user memory which has the same lifetime as the handle.

The OCIEnvCreate() and OCIEnvInit() calls have a similar parameter for allocating user memory which has the same lifetime as the environment handle.

Creating the OCI Environment

Each OCI function call is executed in the context of an environment that is created with the OCIEnvCreate() call. This call must be invoked before any other OCI call is executed. The only exception is the setting of a process-level attribute for the OCI shared mode.

The mode parameter of OCIEnvCreate() specifies whether the application calling the OCI library functions will:

• Run in a threaded environment (mode = OCI_THREADED).

• Use objects (mode = OCI_OBJECT). Use with AQ subscription registration.

• Use subscriptions (mode = OCI_EVENTS).

The mode can be set independently in each environment.

It is necessary to initialize in object mode if the application binds and defines objects, or if it uses the OCI's object navigation calls. The program may also choose to use none of these features (mode = OCI_DEFAULT) or some combination of them, separating the options with a vertical bar. For example if mode = (OCI_THREADED | OCI_OBJECT), then the application runs in a threaded environment and uses objects.

You can specify user-defined memory management functions for each OCI environment.

Allocating Handles and Descriptors

Oracle provides OCI functions to allocate and deallocate handles and descriptors. You must allocate handles using OCIHandleAlloc() before passing them into an OCI call, unless the OCI call, such as OCIBindByPos(), allocates the handles for you.

You can allocate the types of handles listed in Table 2-1, "OCI Handle Types" with OCIHandleAlloc() Depending on the functionality of your application, it needs to allocate some or all of these handles.

Application Initialization, Connection, and Session Creation

An application must call OCIEnvNlsCreate() to initialize the OCI environment handle. Existing applications may have used OCIEnvCreate().

Following this step, the application has several options for establishing a server connection and beginning a user session.

OCILogon2(envhp, errhp, &svchp, (text *)"hr", (ub4)strlen("hr"), (text *)"hr",
          (ub4)strlen("hr"), (text *)"oracledb", (ub4)strlen("oracledb"),
          OCI_DEFAULT);

ALTER USER <targetuser> GRANT CONNECT THROUGH <proxy> [AUTHENTICATION REQUIRED];

#include <oci.h>
...
main()
{
...
OCIEnv     *myenvhp;    /* the environment handle */
OCIServer  *mysrvhp;    /* the server handle */
OCIError   *myerrhp;    /* the error handle */
OCISession *myusrhp;    /* user session handle */
OCISvcCtx  *mysvchp;    /* the  service handle */
...
/* initialize the mode to be the threaded and object environment */
(void) OCIEnvCreate(&myenvhp, OCI_THREADED|OCI_OBJECT, (void  *)0,
                    0, 0, 0, (size_t) 0, (void  **)0);

     /* allocate a server handle */
(void) OCIHandleAlloc ((void  *)myenvhp, (void  **)&mysrvhp,
      OCI_HTYPE_SERVER, 0, (void  **) 0);

      /* allocate an error handle */
(void) OCIHandleAlloc ((void  *)myenvhp, (void  **)&myerrhp,
      OCI_HTYPE_ERROR, 0, (void  **) 0);

      /* create a server context */
(void) OCIServerAttach (mysrvhp, myerrhp, (text *)"inst1_alias",
      strlen ("inst1_alias"), OCI_DEFAULT);

     /* allocate a service handle */
(void) OCIHandleAlloc ((void  *)myenvhp, (void  **)&mysvchp,
      OCI_HTYPE_SVCCTX, 0, (void  **) 0);

 /* set the server attribute in the service context handle*/
(void) OCIAttrSet ((void  *)mysvchp, OCI_HTYPE_SVCCTX,
       (void  *)mysrvhp, (ub4) 0, OCI_ATTR_SERVER, myerrhp);

      /* allocate a user session handle */
(void) OCIHandleAlloc ((void  *)myenvhp, (void  **)&myusrhp,
     OCI_HTYPE_SESSION, 0, (void  **) 0);

      /* set user name attribute in user session handle */
 (void) OCIAttrSet ((void  *)myusrhp, OCI_HTYPE_SESSION,
      (void  *)"hr", (ub4)strlen("hr"),
      OCI_ATTR_USERNAME, myerrhp);

      /* set password attribute in user session handle */
 (void) OCIAttrSet ((void  *)myusrhp, OCI_HTYPE_SESSION,
      (void  *)"hr", (ub4)strlen("hr"),
      OCI_ATTR_PASSWORD, myerrhp);

 (void) OCISessionBegin ((void  *) mysvchp, myerrhp, myusrhp,
      OCI_CRED_RDBMS, OCI_DEFAULT);

    /* set the user session attribute in the service context handle*/
 (void) OCIAttrSet ((void  *)mysvchp, OCI_HTYPE_SVCCTX,
       (void  *)myusrhp, (ub4) 0, OCI_ATTR_SESSION, myerrhp);
...
}

Processing SQL Statements in OCI

A chapter of this manual outlines the specific steps involved in processing SQL statements in OCI.

Return and Error Codes for Data

In Table 2-4, the OCI return code, error number, indicator variable, and column return code are specified when the data fetched is normal, null, or truncated.

For truncated data, data_len is the actual length of the data that has been truncated if this length is less than or equal to SB2MAXVAL. Otherwise, the indicator is set to -2.

Functions Returning Other Values

Some functions return values other than the OCI error codes listed in Table 2-3. When using these function be aware that they return values directly from the function call, rather than through an OUT parameter. More detailed information about each function and its return values is listed in the reference chapters.

Parameter Types

OCI functions take a variety of different types of parameters, including integers, handles, and character strings. Special considerations must be taken into account for some types of parameters, as described in the following sections.

Inserting Nulls into a Column

You can insert a null into a database column in several ways.

1. One method is to use a literal NULL in the text of an INSERT or UPDATE statement. For example, the SQL statement

INSERT INTO emp1 (ename, empno, deptno)
        VALUES (NULL, 8010, 20)

makes the ENAME column NULL.

1. Use indicator variables in the OCI bind call.

   See Also:

   "Indicator Variables"

2. Insert a NULL is to set the buffer length and maximum length parameters both to zero on a bind call.

   Note:

   Following SQL92 requirements, Oracle returns an error if an attempt is made to fetch a null select-list item into a variable that does not have an associated indicator variable specified in the define call.

Indicator Variables

Each bind and define OCI call has a parameter that associates an indicator variable, or an array of indicator variables, with a DML statement, a PL/SQL statement, or a query.

The C language does not have the concept of null values; therefore you associate indicator variables with input variables to specify whether the associated placeholder is a NULL. When data is passed to Oracle, the values of these indicator variables determine whether or not a NULL is assigned to a database field.

For output variables, indicator variables determine whether the value returned from Oracle is a NULL or a truncated value. In the case of a NULL fetch in an OCIStmtFetch() call, or a truncation in an OCIStmtExecute() call, the OCI call returns OCI_SUCCESS_WITH_INFO. The output indicator variable is set.

The datatype of indicator variables is sb2. In the case of arrays of indicator variables, the individual array elements should be of type sb2.

Canceling Calls

On most operating systems, you can cancel long-running or repeated OCI calls, by entering the operating system's interrupt character (usually CTRL-C) from the keyboard.

When you cancel the long-running or repeated call using the operating system interrupt, the error code ORA-01013 ("user requested cancel of current operation") is returned.

Given a particular service context pointer or server context pointer, the OCIBreak() function performs an immediate (asynchronous) stop of any currently executing OCI function associated with the server. It is normally used to stop a long-running OCI call being processed on the server. The OCIReset() function is necessary to perform a protocol synchronization on a nonblocking connection after an OCI application stops a function with OCIBreak().

The status of potentially long-running calls can be monitored through the use of nonblocking calls. Use multithreading for new applications.

Positioned Updates and Deletes

You can use the ROWID associated with a SELECT...FOR UPDATE OF... statement in a later UPDATE or DELETE statement. The ROWID is retrieved by calling OCIAttrGet() on the statement handle to retrieve the handle's OCI_ATTR_ROWID attribute.

For example, for a SQL statement such as

SELECT ename FROM emp1 WHERE empno = 7499 FOR UPDATE OF sal

when the fetch is performed, the ROWID attribute in the handle contains the row identifier of the selected row. You can retrieve the ROWID into a buffer in your program by calling OCIAttrGet() as follows:

OCIRowid *rowid;   /* the rowid in opaque format */
/* allocate descriptor with OCIDescriptorAlloc() */
status = OCIDescriptorAlloc ((void  *) envhp, (void  **) &rowid,
     (ub4) OCI_DTYPE_ROWID, (size_t) 0, (void  **) 0);
status = OCIAttrGet ((void *) mystmtp, OCI_HTYPE_STMT,
     (void *) rowid, (ub4 *) 0, OCI_ATTR_ROWID, (OCIError *) myerrhp);

You can then use the saved ROWID in a DELETE or UPDATE statement. For example, if rowid is the buffer in which the row identifier has been saved, you can later process a SQL statement such as

UPDATE emp1 SET sal = :1 WHERE rowid = :2

by binding the new salary to the :1 placeholder and rowid to the :2 placeholder. Be sure to use datatype code 104 (ROWID descriptor) when binding rowid to :2.

Using prefetching, an array of ROWIDs can be selected for use in subsequent batch updates.

Reserved Words

Some words are reserved by Oracle. That is, they have a special meaning to Oracle and cannot be redefined. For this reason, you cannot use them to name database objects such as columns, tables, or indexes.

Nonblocking Mode in OCI

Because nonblocking mode increases the number of round trips and the CPU usage, use multithreaded calls for new applications.

The OCI provides the ability to establish a server connection in blocking mode or nonblocking mode. When a connection is made in blocking mode, an OCI call returns control to an OCI client application only when the call completes, either successfully or in error. With the nonblocking mode, control is immediately returned to the OCI program if the call could not complete, and the call returns a value of OCI_STILL_EXECUTING.

In nonblocking mode, an application must test the return code of each OCI function to see if it returns OCI_STILL_EXECUTING. If it does, the OCI client can continue to process program logic while waiting to retry the OCI call to the server. This mode is particularly useful in Graphical User Interface (GUI) applications, real-time applications, and in distributed environments.

The nonblocking mode is not interrupt-driven. Rather, it is based on a polling paradigm, which means that the client application has to check whether the pending call is finished at the server by executing the call again with the exact same parameters.

The following features and functions are not supported in nonblocking mode:

• Direct Path Loader

• LOB buffering

• objects

• query cache

• scrollable cursors

• TAF

• OCIAQEnqArray()

• OCIAQDeqArray()

• OCIDescribeAny()

• OCILobArrayRead()

• OCILobArrayWrite()

• OCITransStart()

• OCITransDetach()

Setting Blocking Modes

You can modify or check an application's blocking status by calling OCIAttrSet() to set the status, or OCIAttrGet() to read the status on the server context handle with the attrtype parameter set to OCI_ATTR_NONBLOCKING_MODE. You must set this attribute only after OCISessionBegin() or OCILogon2() has been called. Otherwise, an error will be returned.

Canceling a Nonblocking Call

You can cancel a long-running OCI call by using the OCIBreak() function while the OCI call is in progress. You must then issue an OCIReset() call to reset the asynchronous operation and protocol.

Client Character Set Control from OCI

The function OCIEnvNlsCreate() enables you to set character set information in applications, independently from NLS_LANG and NLS_NCHAR settings. One application can have several environment handles initialized within the same system environment using different client side character set IDs and national character set IDs.

OCIEnvNlsCreate(OCIEnv **envhp, ..., csid, ncsid); 

where csid is the value for character set ID, and ncsid is the value for national character set ID. Either can be 0 or OCI_UTF16ID. If both are 0, this is equivalent to using OCIEnvCreate() instead. The other arguments are the same as for the OCIEnvCreate() call.

OCIEnvNlsCreate() is an enhancement for programmatic control of character sets, because it validates OCI_UTF16ID.

When character set IDs are set through the function OCIEnvNlsCreate(), they will replace the settings in NLS_LANG and NLS_NCHAR. In addition to all character sets supported by NLSRTL, OCI_UTF16ID is also allowed as a character set ID in the OCIEnvNlsCreate() function, although this ID is not valid in NLS_LANG or NLS_NCHAR.

Any Oracle character set ID, except AL16UTF16, can be specified through the OCIEnvNlsCreate() function to specify the encoding of metadata, SQL CHAR data, and SQL NCHAR data.

You can retrieve character sets in NLS_LANG and NLS_NCHAR through another function, OCINlsEnvironmentVariableGet().

Code Example for Character Set Control in OCI

For a pseudocode fragment that illustrates a sample usage of these calls:

Character Control and OCI Interfaces

OCINlsGetInfo() returns information about OCI_UTF16ID if this value has been used in OCIEnvNlsCreate().

OCIAttrGet() returns the character set ID and national character set ID that were passed into OCIEnvNlsCreate(). This is used to get OCI_ATTR_ENV_CHARSET_ID and OCI_ATTR_ENV_NCHARSET_ID. This includes the value OCI_UTF16ID.

If both charset and ncharset parameters were set to NULL by OCIEnvNlsCreate(), the character set IDs in NLS_LANG and NLS_NCHAR will be returned.

OCIAttrSet() sets character IDs as the defaults if OCI_ATTR_CHARSET_FORM is reset through this function. The eligible character set IDs include OCI_UTF16ID if OCIEnvNlsCreate() has it passed as charset or ncharset.

OCIBindByName() and OCIBindByPos() bind variables with default character set in the OCIEnvNlsCreate() call, including OCI_UTF16ID. The actual length and the returned length are always in bytes if OCIEnvNlsCreate() is used.

OCIDefineByPos() defines variables with the value of charset in OCIEnvNlsCreate(), including OCI_UTF16ID, as the default. The actual length and returned length are always in bytes if OCIEnvNlsCreate() is used. This behavior for bind and define handles is different from that when OCIEnvCreate() is used and OCI_UTF16ID is the character set ID for the bind and define handles.

Character Length Semantics in OCI

OCI works as a translator between server and client, and passes around character information for constraint checking.

There are two kinds of character sets, variable-width and fixed-width, as a single byte character set is just a special case of a fixed-width character set where each byte stands for one character.

For fixed-width character sets, constraint checking is easier as number of bytes is simply equal to a multiple of number of characters. Therefore, no scanning of the entire string is needed to determine the number of characters for fixed-width character sets. However, for variable-width ones, complete scanning is needed to determine the number of characters.

Character Set Support in OCI

See "Character Length Semantics Support in Describing" and "Character Conversion in OCI Binding and Defining" for a complete discussion.

Other OCI Globalization Support Functions

Many globalization support functions accept either the environment handle or the user session handle. The OCI environment handle is associated with the client NLS environment variables. This environment does not change when ALTER SESSION statements are issued to the server. The character set associated with the environment handle is the client character set. The OCI session handle (returned by OCISessionBegin()) is associated with the server session environment. The NLS settings change when the session environment is modified with an ALTER SESSION statement. The character set associated with the session handle is the database character set.

Note that the OCI session handle does not have NLS settings associated with it until the first transaction begins in the session. SELECT statements do not begin a transaction.

For complete details and discussions of the functions that follow:

Getting Locale Information in OCI

An Oracle locale consists of language, territory, and character set definitions. The locale determines conventions such as day and month names, as well as date, time, number, and currency formats. A globalized application follows a user's locale setting and cultural conventions. For example, when the locale is set to German, users expect to see day and month names in German.

You can retrieve the following information with the OCINlsGetInfo() function:

• Days of the week (translated)

• Abbreviated days of the week (translated)

• Month names (translated)

• Abbreviated month names (translated)

• Yes/no (translated)

• AM/PM (translated)

• AD/BC (translated)

• Numeric format

• Debit/credit

• Date format

• Currency formats

• Default language

• Default territory

• Default character set

• Default linguistic sort

• Default calendar

Example of Getting Locale Information in OCI

This example code retrieves information and checks for errors.

sword MyPrintLinguisticName(envhp, errhp)
OCIEnv   *envhp;
OCIError *errhp;
{
  OraText  infoBuf[OCI_NLS_MAXBUFSZ];
  sword ret;
  
  ret = OCINlsGetInfo(envhp,                           /* environment handle */
                      errhp,                                 /* error handle */
                      infoBuf,                         /* destination buffer */
                      (size_t) OCI_NLS_MAXBUFSZ,              /* buffer size */
                      (ub2) OCI_NLS_LINGUISTIC_NAME);                /* item */

  if (ret != OCI_SUCCESS) 
  {
    checkerr(errhp, ret, OCI_HTYPE_ERROR);
    ret = OCI_ERROR; 
  }
  else
  {
    printf("NLS linguistic: %s\n", infoBuf);
   }
  return(ret);
}

Manipulating Strings in OCI

Multibyte strings and wide character strings are supported for string manipulation:

Multibyte strings are encoded in native Oracle character sets. Functions that operate on multibyte strings take the string as a whole unit with the length of the string calculated in bytes. Wide character string (wchar) functions provide more flexibility in string manipulation. They support character-based and string-based operations where the length the string calculated in characters.

The wide character datatype, OCIWchar, is Oracle-specific and should not be confused with the wchar_t datatype defined by the ANSI/ISO C standard. The Oracle wide character datatype is always 4 bytes in all operating systems, while the size of wchar_t depends on the implementation and the operating system. The Oracle wide character datatype normalizes multibyte characters so that they have a uniform fixed width for easy processing. This guarantees no data loss for round trip conversion between the Oracle wide character set and the native character set.

String manipulation can be classified into the following categories:

• Conversion of strings between multibyte and wide character

• Character classifications

• Case conversion

• Calculations of display length

• General string manipulation, such as comparison, concatenation, and searching

  See Also:

  "OCI String Manipulation Functions"

Example of Manipulating Strings in OCI

The following example shows a simple case of manipulating strings.

size_t MyConvertMultiByteToWideChar(envhp, dstBuf, dstSize, srcStr)
OCIEnv     *envhp;
OCIWchar   *dstBuf;
size_t      dstSize;
OraText    *srcStr;                         /* null terminated source string */
{
  sword  ret;
  size_t dstLen = 0;
  size_t srcLen;

  /* get length of source string */
  srcLen = OCIMultiByteStrlen(envhp, srcStr);
  
  ret = OCIMultiByteInSizeToWideChar(envhp,            /* environment handle */
                 dstBuf,                               /* destination buffer */
                 dstSize,                         /* destination buffer size */
                 srcStr,                                    /* source string */
                 srcLen,                          /* length of source string */
                 &dstLen);                  /* pointer to destination length */

  if (ret != OCI_SUCCESS)                                          
  {
    checkerr(envhp, ret, OCI_HTYPE_ENV);                 
  }
  return(dstLen);
}

Example of Classifying Characters in OCI

The OCI character classification functions are described in detail.

The following example shows how to classify characters in OCI.

boolean MyIsNumberWideCharString(envhp, srcStr)
OCIEnv   *envhp;
OCIWchar *srcStr;                                 /* wide char source string */
{
  OCIWchar *pstr = srcStr;                        /* define and init pointer */
  boolean status = TRUE;            /* define and initialize status variable */

  /* Check input */
  if (pstr == (OCIWchar*) NULL)
    return(FALSE);


  if (*pstr == (OCIWchar) NULL)
    return(FALSE);

                                            /* check each character for digit */
  do 
  {
    if (OCIWideCharIsDigit(envhp, *pstr) != TRUE)
    {
      status = FALSE;
      break;                                  /* non-decimal digit character */
    }
  } while ( *++pstr != (OCIWchar) NULL);

  return(status);
}

Converting Character Sets in OCI

Conversion between Oracle character sets and Unicode (16-bit, fixed-width Unicode encoding) is supported. Replacement characters are used if a character has no mapping from Unicode to the Oracle character set. Therefore, conversion back to the original character set is not always possible without data loss.

Character set conversion functions involving Unicode character sets require data bind and define buffers to be aligned at a ub2 address, or else an error is raised.

Example of Converting Character Sets in OCI

The following example shows a simple conversion into Unicode.

/* Example of Converting Character Sets in OCI
--------------------------------------------*/

size_t MyConvertMultiByteToUnicode(envhp, errhp, dstBuf, dstSize, srcStr)
OCIEnv   *envhp;
OCIError *errhp;
ub2 *dstBuf;
size_t dstSize;
OraText *srcStr;
{
  size_t dstLen = 0;
  size_t srcLen = 0;
  OraText tb[OCI_NLS_MAXBUFSZ];   /* NLS info buffer */
  ub2    cid;                     /* OCIEnv character set id */

  /* get OCIEnv character set */
  checkerr(errhp, OCINlsGetInfo(envhp, errhp, tb, sizeof(tb),
                                OCI_NLS_CHARACTER_SET));
  cid = OCINlsCharSetNameToId(envhp, tb);

  if (cid == OCI_UTF16ID)
  {
    ub2    *srcStrUb2 = (ub2*)srcStr;
    while (*srcStrUb2++) ++srcLen;
    srcLen *= sizeof(ub2);
  }
  else
    srcLen = OCIMultiByteStrlen(envhp, srcStr);

  checkerr(errhp,
    OCINlsCharSetConvert(
      envhp,       /* environment handle */
      errhp,       /* error handle */
      OCI_UTF16ID, /* Unicode character set id */
      dstBuf,      /* destination buffer */
      dstSize,     /* size of destination buffer */
      cid,         /* OCIEnv character set id */
      srcStr,      /* source string */
      srcLen,      /* length of source string */
      &dstLen));   /* pointer to destination length */

  return dstLen/sizeof(ub2);
}

OCI Messaging Functions

The user message API provides a simple interface for cartridge developers to retrieve their own messages and Oracle messages.

Example of Retrieving a Message from a Text Message File

This example creates a message handle, initializes it to retrieve messages from impus.msg, retrieves message number 128, and closes the message handle. It assumes that OCI environment handles, OCI session handles, product, facility, and cache size have been initialized properly.

OCIMsg msghnd;                                              /* message handle */
         /* initialize a message handle for retrieving messages from impus.msg*/
err = OCIMessageOpen(hndl,errhp, &msghnd, prod,fac,OCI_DURATION_SESSION);
if (err != OCI_SUCCESS)
                                                            /* error handling */
...
                            /* retrieve the message with message number = 128 */
msgptr = OCIMessageGet(msghnd, 128, msgbuf, sizeof(msgbuf));
                         /* do something with the message, such as display it */
...
      /* close the message handle when there are no more messages to retrieve */
OCIMessageClose(hndl, errhp, msghnd);

lmsgen Utility

The lmsgen utility converts text-based message files (.msg) into binary format (.msb) so that Oracle messages and OCI messages provided by the user can be returned to OCI functions in the desired language.

lmsgen text_file product facility [language]

/ Copyright (c) 2001 by the Oracle Corporation.  All rights reserved.
/ This is a test us7ascii message file
# CHARACTER_SET_NAME= american_america.us7ascii
/
00000, 00000, "Export terminated unsuccessfully\n"
00003, 00000, "no storage definition found for segment(%lu, %lu)"

$HOME/myApp/mesg/impus.msg

00128,2, "Duplicate entry %s found in %s"

% lmsgen impus.msg $HOME/myApplication imp AMERICAN

Generating message file impus.msg -->
/home/scott/myApplication/mesg/impus.msb

NLS Binary Message File Generation Utility: Version 9.2.0.0.0 -Production

Copyright (c) Oracle Corporation 1979, 2001.  All rights reserved.

CORE    9.2.0.0.0       Production