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Oracle® Call Interface Programmer's Guide
11g Release 2 (11.2)

Part Number E10646-06
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Handle and Descriptor Functions

Table 16-3 lists the OCI handle and descriptor functions that are described in this section.

Table 16-3 Handle and Descriptor Functions  

Function Purpose

"OCIArrayDescriptorAlloc()"

Allocate an array of descriptors

"OCIArrayDescriptorFree()"

Free an array of descriptors

"OCIAttrGet()"

Get the value of an attribute of a handle

"OCIAttrSet()"

Set the value of an attribute of a handle or descriptor

"OCIDescriptorAlloc()"

Allocate and initialize a descriptor or LOB locator

"OCIDescriptorFree()"

Free a previously allocated descriptor

"OCIHandleAlloc()"

Allocate and initialize a handle

"OCIHandleFree()"

Free a previously allocated handle

"OCIParamGet()"

Get a parameter descriptor

"OCIParamSet()"

Set parameter descriptor in COR handle



OCIArrayDescriptorAlloc()

Purpose

Allocates an array of descriptors.

Syntax

sword OCIArrayDescriptorAlloc ( const  void   *parenth,
                                void          **descpp, 
                                const ub4     type,
                                ub4           array_size,
                                const size_t  xtramem_sz,
                                void          **usrmempp);

Parameters

parenth (IN)

An environment handle.

descpp (OUT)

Returns a pointer to a contiguous array of descriptors of the desired type.

type (IN)

Specifies the type of descriptor or LOB locator to be allocated. For a list of types, see "OCIDescriptorAlloc()".

array_size (IN)

Specifies the number of descriptors to allocate. An error is thrown when the call cannot allocate the number of descriptors.

xtramem_sz (IN)

Specifies an amount of user memory to be allocated for use by the application for the lifetime of the descriptors.

usrmempp (OUT)

Returns a pointer to the user memory of size xtramem_sz allocated by the call for the user for the lifetime of the descriptors.

Comments

This call returns OCI_SUCCESS if successful, or a suitable error if an out-of-memory condition occurs.

See Also:

"User Memory Allocation" for more information about the xtramem_sz parameter and user memory allocation

Example

This example can be modified to allocate a large number of descriptors.

OCIDateTime *descpp1[500];
...
for (i = 0; i!=500; i++)
{
     /* Allocate descriptors */
OCIDescriptorAlloc((void  *)envhp,(void  **)&descpp1[i], OCI_DTYPE_TIMESTAMP_TZ,
                   0,(void  **)0);
}
...

The for loop can now be replaced with a single call:

OCIArrayDescriptorAlloc((void *)envhp,(void **)&descpp1,
                        OCI_DTYPE_TIMESTAMP_TZ, 500, 0, (void **)0);

Related Functions

OCIDescriptorAlloc(), OCIArrayDescriptorFree()


OCIArrayDescriptorFree()

Purpose

Free a previously allocated array of descriptors.

Syntax

sword OCIArrayDescriptorFree ( void       **descp,
                               const ub4  type );

Parameters

descp (IN)

Pointer to an array of allocated descriptors.

type (IN)

Specifies the type of storage to be freed. See the types listed in "OCIDescriptorAlloc()".

Comments

An error is returned when a descriptor is allocated using OCIDescriptorAlloc(), but freed using OCIArrayDescriptorFree().

Descriptors allocated using OCIArrayDescriptorAlloc() must be freed using OCIArrayDescriptorFree(). You must be careful to free the entire array at once: pass in the pointer descpp returned by OCIArrayDescriptorAlloc() to OCIArrayDescriptorFree() appropriately. Otherwise, there can be memory leaks.

Related Functions

OCIArrayDescriptorAlloc()


OCIAttrGet()

Purpose

Gets the value of an attribute of a handle.

Syntax

sword OCIAttrGet ( const void     *trgthndlp,
                   ub4            trghndltyp,
                   void           *attributep,
                   ub4            *sizep,
                   ub4            attrtype,
                   OCIError       *errhp );

Parameters

trgthndlp (IN)

Pointer to a handle type. The actual handle can be a statement handle, a session handle, and so on. When this call is used to get encoding, users are allowed to check against either an environment or statement handle.

trghndltyp (IN)

The handle type. Valid types are:

attributep (OUT)

Pointer to the storage for an attribute value. Is in the encoding specified by the charset parameter of a previous call to OCIEnvNlsCreate().

sizep (OUT)

The size of the attribute value, always in bytes because attributep is a void pointer. This can be passed as NULL for most attributes because the sizes of non-string attributes are already known by the OCI library. For text* parameters, a pointer to a ub4 must be passed in to get the length of the string.

attrtype (IN)

The type of attribute being retrieved. The handle types and their readable attributes are listed in Appendix A.

errhp (IN/OUT)

An error handle that you can pass to OCIErrorGet() for diagnostic information when there is an error.

Comments

This call is used to get a particular attribute of a handle. OCI_DTYPE_PARAM is used to do implicit and explicit describes. The parameter descriptor is also used in direct path loading. For implicit describes, the parameter descriptor has the column description for each select list. For explicit describes, the parameter descriptor has the describe information for each schema object that you are trying to describe. If the top-level parameter descriptor has an attribute that is itself a descriptor, use OCI_ATTR_PARAM as the attribute type in the subsequent call to OCIAttrGet() to get the Unicode information in an environment or statement handle.

A function closely related to OCIAttrGet() is OCIDescribeAny(), which is a generic describe call that describes existing schema objects: tables, views, synonyms, procedures, functions, packages, sequences, and types. As a result of this call, the describe handle is populated with the object-specific attributes that can be obtained through an OCIAttrGet() call.

Then an OCIParamGet() call on the describe handle returns a parameter descriptor for a specified position. Parameter positions begin with 1. Calling OCIAttrGet() on the parameter descriptor returns the specific attributes of a stored procedure or function parameter or a table column descriptor. These subsequent calls do not need an extra round-trip to the server because the entire schema object description is cached on the client side by OCIDescribeAny(). Calling OCIAttrGet() on the describe handle can also return the total number of positions.

In UTF-16 mode, particularly when executing a loop, try to reuse the same pointer variable corresponding to an attribute and copy the contents to local variables after OCIAttrGet() is called. If multiple pointers are used for the same attribute, a memory leak can occur.

Related Functions

OCIAttrSet()


OCIAttrSet()

Purpose

Sets the value of an attribute of a handle or a descriptor.

Syntax

sword OCIAttrSet ( void        *trgthndlp,
                   ub4         trghndltyp,
                   void        *attributep,
                   ub4         size,
                   ub4         attrtype,
                   OCIError    *errhp );

Parameters

trgthndlp (IN/OUT)

Pointer to a handle whose attribute gets modified.

trghndltyp (IN/OUT)

The handle type.

attributep (IN)

Pointer to an attribute value. The attribute value is copied into the target handle. If the attribute value is a pointer, then only the pointer is copied, not the contents of the pointer. String attributes must be in the encoding specified by the charset parameter of a previous call to OCIEnvNlsCreate().

size (IN)

The size of an attribute value. This can be passed in as 0 for most attributes, as the size is already known by the OCI library. For text* attributes, a ub4 must be passed in set to the length of the string in bytes, regardless of encoding.

attrtype (IN)

The type of attribute being set.

errhp (IN/OUT)

An error handle that you can pass to OCIErrorGet() for diagnostic information when there is an error.

Comments

See Appendix A for a list of handle types and their writable attributes.

Related Functions

OCIArrayDescriptorAlloc()


OCIDescriptorAlloc()

Purpose

Allocates storage to hold descriptors or LOB locators.

Syntax

sword OCIDescriptorAlloc ( const void    *parenth,
                           void          **descpp, 
                           ub4           type,
                           size_t        xtramem_sz,
                           void          **usrmempp);

Parameters

parenth (IN)

An environment handle.

descpp (OUT)

Returns a descriptor or LOB locator of the desired type.

type (IN)

Specifies the type of descriptor or LOB locator to be allocated:

xtramem_sz (IN)

Specifies an amount of user memory to be allocated for use by the application for the lifetime of the descriptor.

usrmempp (OUT)

Returns a pointer to the user memory of size xtramem_sz allocated by the call for the user for the lifetime of the descriptor.

Comments

Returns a pointer to an allocated and initialized descriptor, corresponding to the type specified in type. A non-NULL descriptor or LOB locator is returned on success. No diagnostics are available on error.

This call returns OCI_SUCCESS if successful, or OCI_INVALID_HANDLE if an out-of-memory error occurs.

See Also:

"User Memory Allocation" for more information about the xtramem_sz parameter and user memory allocation

Related Functions

OCIDescriptorFree(), OCIArrayDescriptorAlloc(), OCIArrayDescriptorFree()


OCIDescriptorFree()

Purpose

Deallocates a previously allocated descriptor.

Syntax

sword OCIDescriptorFree ( void     *descp,
                          ub4      type );

Parameters

descp (IN)

An allocated descriptor.

type (IN)

Specifies the type of storage to be freed. See the types listed in "OCIDescriptorAlloc()".

Comments

This call frees storage associated with a descriptor. Returns OCI_SUCCESS or OCI_INVALID_HANDLE. All descriptors can be explicitly deallocated; however, OCI deallocates a descriptor if the environment handle is deallocated.

Related Functions

OCIDescriptorAlloc()


OCIHandleAlloc()

Purpose

Returns a pointer to an allocated and initialized handle.

Syntax

sword OCIHandleAlloc ( const void    *parenth,
                       void          **hndlpp, 
                       ub4           type, 
                       size_t        xtramem_sz,
                       void          **usrmempp );

Parameters

parenth (IN)

An environment handle.

hndlpp (OUT)

Returns a handle.

type (IN)

Specifies the type of handle to be allocated. The allowed handles are described in Table 2-1.

xtramem_sz (IN)

Specifies an amount of user memory to be allocated.

usrmempp (OUT)

Returns a pointer to the user memory of size xtramem_sz allocated by the call for the user.

Comments

Returns a pointer to an allocated and initialized handle, corresponding to the type specified in type. A non-NULL handle is returned on success. All handles are allocated with respect to an environment handle that is passed in as a parent handle.

No diagnostics are available on error. This call returns OCI_SUCCESS if successful, or OCI_INVALID_HANDLE if an error occurs.

Handles must be allocated using OCIHandleAlloc() before they can be passed into an OCI call.

See Also:

"User Memory Allocation" for more information about using the xtramem_sz parameter for user memory allocation

Related Functions

OCIHandleFree()


OCIHandleFree()

Purpose

This call explicitly deallocates a handle.

Syntax

sword OCIHandleFree ( void      *hndlp,
                      ub4       type );

Parameters

hndlp (IN)

A handle allocated by OCIHandleAlloc().

type (IN)

Specifies the type of storage to be freed. The handles are described in Table 2-1.

Comments

This call frees up storage associated with a handle, corresponding to the type specified in the type parameter.

This call returns either OCI_SUCCESS, OCI_INVALID_HANDLE, or OCI_ERROR.

All handles may be explicitly deallocated. The OCI deallocates a child handle if the parent is deallocated.

When a statement handle is freed, the cursor associated with the statement handle is closed, but the actual cursor closing may be deferred to the next round-trip to the server. If the application must close the cursor immediately, you can make a server round-trip call, such as OCIServerVersion() or OCIPing(), after the OCIHandleFree() call.

Related Functions

OCIHandleAlloc()


OCIParamGet()

Purpose

Returns a descriptor of a parameter specified by position in the describe handle or statement handle.

Syntax

sword OCIParamGet ( const void        *hndlp,
                    ub4               htype,
                    OCIError          *errhp,
                    void              **parmdpp,
                    ub4               pos );

Parameters

hndlp (IN)

A statement handle or describe handle. The OCIParamGet() function returns a parameter descriptor for this handle.

htype (IN)

The type of the handle passed in the hndlp parameter. Valid types are:

errhp (IN/OUT)

An error handle that you can pass to OCIErrorGet() for diagnostic information when there is an error.

parmdpp (OUT)

A descriptor of the parameter at the position given in the pos parameter, of handle type OCI_DTYPE_PARAM.

pos (IN)

Position number in the statement handle or describe handle. A parameter descriptor is returned for this position.

Note:

OCI_ERROR is returned if there are no parameter descriptors for this position.

Comments

This call returns a descriptor of a parameter specified by position in the describe handle or statement handle. Parameter descriptors are always allocated internally by the OCI library. They can be freed using OCIDescriptorFree(). For example, if you fetch the same column metadata for every execution of a statement, then the program leaks memory unless you explicitly free the parameter descriptor between each call to OCIParamGet().

See Also:

Appendix A for more detailed information about parameter descriptor attributes

Related Functions

OCIArrayDescriptorAlloc(), OCIAttrSet(), OCIParamSet(), OCIDescriptorFree()


OCIParamSet()

Purpose

Sets a complex object retrieval (COR) descriptor into a COR handle.

Syntax

sword OCIParamSet ( void           *hndlp,
                    ub4            htype,
                    OCIError       *errhp,
                    const void     *dscp,
                    ub4            dtyp,
                    ub4            pos );

Parameters

hndlp (IN/OUT)

Handle pointer.

htype (IN)

Handle type.

errhp (IN/OUT)

An error handle that you can pass to OCIErrorGet() for diagnostic information when there is an error.

dscp (IN)

Complex object retrieval descriptor pointer.

dtyp (IN)

Descriptor type. The descriptor type for a COR descriptor is OCI_DTYPE_COMPLEXOBJECTCOMP.

pos (IN)

Position number.

Comments

The COR handle must have been previously allocated using OCIHandleAlloc(), and the descriptor must have been previously allocated using OCIDescriptorAlloc(). Attributes of the descriptor are set using OCIAttrSet().

See Also:

"Complex Object Retrieval" for more information about complex object retrieval

Related Functions

OCIParamGet()