Release 8.1.6
Part Number A76975-01
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| Oracle Call Interface Programmer's Guide Release 8.1.6 Part Number A76975-01 |
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The OCI datatype mapping and manipulation functions provide OCI programs with the ability to manipulate instances of Oracle predefined datatypes in a C application. This chapter discusses those functions, and also includes information about how object types are stored in the database. For information about bind and define operations using the Oracle C datatypes, refer to Chapter 12, "Binding and Defining in Object Applications".
The following topics are covered in this chapter:
The OCI datatype mapping and manipulation functions provide the ability to manipulate instances of predefined Oracle C datatypes. These datatypes are used to represent the attributes of user-defined datatypes, including object types in Oracle.
Each group of functions within the OCI is distinguished by a particular naming convention. The datatype mapping and manipulation functions, for example, can be easily recognized because the function names start with the prefix OCI, followed by the name of a datatype, as in OCIDateFromText() and OCIRawSize(). As will be explained later, the names can be further broken down into function groups that operate on a particular type of data.
Additionally, the predefined Oracle C types on which these functions operate are also distinguished by names which begin with the prefix OCI, as in OCIDate or OCIString.
The datatype mapping and manipulation functions are used when an application needs to manipulate, bind, or define attributes of objects that are stored in an Oracle database, or which have been retrieved by a SQL query. Retrieved objects are stored in the client-side object cache, as was described in Chapter 13, "Object Cache and Object Navigation".
This chapter describes the purpose and structure of each of the datatypes that can be manipulated by the OCI datatype mapping and manipulation functions. It also summarizes the different function groups, and gives lists of available functions and their purposes.
This chapter also provides information about how to use these datatypes in bind and define operations within an OCI application.
These functions are valid only when an OCI application is running in object mode. For information about initializing the OCI in object mode, and creating an OCI application that accesses and manipulates objects, refer to the section "Initializing Environment and Object Cache".
For detailed information about object types, attributes, and collection datatypes, refer to Oracle8i Concepts.
Oracle provides a rich set of predefined datatypes with which you can create tables and specify user-defined datatypes (including object types). Object types extend the functionality of Oracle by allowing you to create datatypes that precisely model the types of data with which they work. This can provide increased efficiency and ease-of-use for programmers who are accessing the data.
Database tables and object types are based upon the datatypes supplied by Oracle. These tables and types are created with SQL statements and stored using a specific set of Oracle internal datatypes, like VARCHAR2 or NUMBER. For example, the following SQL statements create a user-defined address datatype and an object table to store instances of that type:
CREATE TYPE address AS OBJECT (street1 varchar2(50), street2 varchar2(50), city varchar2(30), state char(2), zip number(5)); CREATE TABLE address_table OF address;
The new address type could also be used to create a regular table with an object column:
CREATE TABLE employees (name varchar2(30), birthday date, home_addr address);
An OCI application can manipulate information in the name and birthday columns of the employees table using straightforward bind and define operations in association with SQL statements. Accessing information stored as attributes of objects requires some extra steps.
The OCI application first needs a way to represent the objects in a C-language format. This is accomplished by using the Object Type Translator (OTT) to generate C struct representations of user-defined types. The elements of these structs have datatypes that represent C language mappings of Oracle datatypes. The following table lists the available Oracle types you can use as object attribute types and their C mappings:
An additional C type, OCIInd, is used to represent null indicator information corresponding to attributes of object types.
See Also: For more information and examples regarding the use of the OTT, refer to Chapter 14, "Using the Object Type Translator".
Oracle followed a distinct design philosophy when specifying the mappings of Oracle predefined types. The current system has the following benefits and advantages:
In an OCI application, the manipulation of data may be as simple as adding together two integer variables and storing the result in a third variable:
int int_1, int_2, sum; ... /* some initialization occurs */ ... sum = int_1 + int_2;
The C language provides a set of predefined operations on simple types like integer. However, the C datatypes listed in Table 11-1, "C Language Mappings of Object Type Attributes" are not simple C primitives. Types like OCIString and OCINumber are actually structs with a specific Oracle-defined internal structure. It is not possible to simply add together two OCINumbers and store the value in the third.
The following is not valid:
OCINumber num_1, num_2, sum; ... /* some initialization occurs */ ... sum = num_1 + num_2; /* NOT A VALID OPERATION */
The OCI datatype mapping and manipulation functions are provided to enable you to perform operations on these new datatypes. For example, the above addition of OCINumbers could be accomplished as follows, using the OCINumberAdd() function:
OCINumber num_1, num_2, sum; ... /* some initialization occurs */ ... OCINumberAdd(errhp, &num_1, &num_2, &sum): /* errhp is error handle */
The OCI provides functions to operate on each of the new datatypes. The names of the functions provide information about the datatype on which they operate. The first three letters, OCI, indicate that the function is part of the OCI. The next part of the name indicates the datatype on which the function operates. The following table shows the various function prefixes, along with example function names and the datatype on which those functions operate:
The structure of each of the datatypes is described later in this chapter, along with a list of the functions that manipulate that type.
Oracle numbers have a precision of 38 decimal digits. All Oracle number operations are accurate to the full precision, with the following exceptions:
The Oracle date format is mapped in C by the OCIDate type, which is an opaque C struct. Elements of the struct represent the year, month, day, hour, minute, and second of the date. The specific elements can be set and retrieved using the appropriate OCI functions.
The OCIDate datatype can be bound or defined directly using the external typecode SQLT_ODT in the bind or define call.
The OCI date manipulation functions are listed in the following tables, which are organized according to functionality. Unless otherwise specified, the term date in these tables refers to a value of type OCIDate.
See Also: The prototypes and descriptions for all the functions are provided in Chapter 17, "OCI Datatype Mapping and Manipulation Functions".
The following functions perform date conversion.
| Function | Purpose |
|---|---|
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OCIDateToText() |
convert date to string |
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OCIDateFromText() |
convert text string to date |
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OCIDateZoneToZone() |
convert date from one time zone to another |
The following functions retrieve and assign date elements.
The following functions perform date arithmetic and comparison.
| Function | Purpose |
|---|---|
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OCIDateAddDays() |
add days |
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OCIDateAddMonths() |
add months |
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OCIDateCompare() |
compare dates |
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OCIDateDaysBetween() |
calculate the number of days between two dates |
The following functions access date information.
| Function | Purpose |
|---|---|
|
OCIDateLastDay() |
the last day of the month |
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OCIDateNextDay() |
the first named day after a given date |
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OCIDateSysDate() |
the system date |
The following function checks date validity.
| Function | Purpose |
|---|---|
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OCIDateCheck() |
check whether a given date is valid |
The following code provides examples of how to manipulate an attribute of type OCIDate using OCI calls.
#define FMT "DAY, MONTH DD, YYYY" #define LANG "American" struct person { OCIDate start_date; }; typedef struct person person; OCIError *err; person *tim; sword status; /* error status */ uword invalid; OCIDate last_day, next_day; text buf[100], last_day_buf[100], next_day_buf[100]; ub4 buflen = sizeof(buf); /* For this example, assume the OCIEnv and OCIError have been * initialized as described in Chapter 2. */ /* Pin tim person object in the object cache. See Chapter 13 for * information about pinning. For this example, assume that * tim is pointing to the pinned object. */ /* set the start date of tim */ OCIDateSetTime(&tim->start_date,8,0,0); OCIDateSetDate(&tim->start_date,1990,10,5) /* check if the date is valid */ if (OCIDateCheck(err, &tim->start_date, &invalid) != OCI_SUCCESS) /* error handling code */ if (invalid) /* error handling code */ /* get the last day of start_date's month */ if (OCIDateLastDay(err, &tim->start_date, &last_day) != OCI_SUCCESS) /* error handling code */ /* get date of next named day */ if (OCIDateNextDay(err, &tim->start_date, "Wednesday", strlen("Wednesday"), &next_day) != OCI_SUCCESS) /* error handling code */ /* convert dates to strings and print the information out */ /* first convert the date itself*/ buflen = sizeof(buf); if (OCIDateToText(err, &tim->start_date, FMT, sizeof(FMT)-1, LANG, sizeof(LANG)-1, &buflen, buf) != OCI_SUCCESS) /* error handling code */ /* now the last day of the month */ buflen = sizeof(last_day_buf); if (OCIDateToText(err, &last_day, FMT, sizeof(FMT)-1, LANG, sizeof(LANG)-1, &buflen, last_day_buf) != OCI_SUCCESS) /* error handling code */ /* now the first Wednesday after this date */ buflen = sizeof(next_day_out); if (OCIDateToText(err, &next_day, FMT, sizeof(FMT)-1, LANG, sizeof(LANG)-1, &buflen, next_day_buf) != OCI_SUCCESS) /* error handling code */ /* print out the info */ printf("For: %s\n", buf); printf("The last day of the month is: %s\n", last_day_buf); printf("The next Wednesday is: %s\n", next_day_buf);
The output will be:
For: Monday, May 13, 1996 The last day of the month is: Friday, May 31 The next Wednesday is: Wednesday, May 15
The OCINumber datatype is an opaque structure used to represent Oracle numeric datatypes (NUMBER, FLOAT, DECIMAL, and so forth). You can bind or define this type using the external typecode SQLT_VNU in the bind or define call.
The OCINumber manipulation functions are listed in the following tables, which are organized according to functionality. Unless otherwise specified, the term number in these tables refers to a value of type OCINumber.
See Also: The prototypes and descriptions for all the functions are provided in Chapter 17, "OCI Datatype Mapping and Manipulation Functions".
The following functions perform arithmetic operations.
The following functions perform conversions between numbers and reals, integers, and strings.
The following functions perform exponential and logarithmic operations.
The following functions perform trigonometric operations on numbers.
The following functions perform assign and compare operations on numbers.
The following example shows how to manipulate an attribute of type OCINumber.
struct person { OCINumber sal; }; typedef struct person person; OCIError *err; person* steve; person* scott; person* jason; OCINumber *stevesal; OCINumber *scottsal; OCINumber *debsal; sword status; int inum; double dnum; OCINumber ornum; char buffer[21]; ub4 buflen; sword result; /* For this example, assume OCIEnv and OCIError are initialized. */ /* For this example, assume that steve, scott and jason are pointing to person objects which have been pinned in the object cache. */ stevesal = &steve->sal; scottsal = &scott->sal; debsal = &jason->sal; /* initialize steve's salary to be $12,000 */ OCINumberInit(err, stevesal); inum = 12000; status = OCINumberFromInt(err, &inum, sizeof(inum), OCI_NUMBER_SIGNED, stevesal); if (status != OCI_SUCCESS) /* handle error from OCINumberFromInt */; /* initialize scott's salary to be same as steve */ OCINumberAssign(err, stevesal, scottsal); /* initialize jason's salary to be 20% more than steve's */ dnum = 1.2; status = OCINumberFromReal(err, &dnum, DBL_DIG, &ornum); if (status != OCI_SUCCESS) /* handle error from OCINumberFromReal */; status = OCINumberMul(err, stevesal, &ornum, debsal); if (status != OCI_SUCCESS) /* handle error from OCINumberMul */; /* give scott a 50% raise */ dnum = 1.5; status = OCINumberFromReal(err, &dnum, DBL_DIG, &ornum); if (status != OCI_SUCCESS) /* handle error from OCINumberFromReal */; status = OCINumberMul(err, scottsal, &ornum, scottsal); if (status != OCI_SUCCESS) /* handle error from OCINumberMul */; /* double steve's salary */ status = OCINumberAdd(err, stevesal, stevesal, stevesal); if (status != OCI_SUCCESS) /* handle error from OCINumberAdd */; /* get steve's salary in integer */ status = OCINumberToInt(err, stevesal, sizeof(inum), OCI_NUMBER_SIGNED, &inum); if (status != OCI_SUCCESS) /* handle error from OCINumberToInt */; /* inum is set to 24000 */ /* get jason's salary in double */ status = OCINumberToReal(err, debsal, sizeof(dnum), &dnum); if (status != OCI_SUCCESS) /* handle error from OCINumberToReal */; /* dnum is set to 14400 */ /* print scott's salary as DEM0001`8000.00 */ buflen = sizeof(buffer); status = OCINumberToText(err, scottsal, "C0999G9999D99", 13, "NLS_NUMERIC_CHARACTERS='.`' NLS_ISO_CURRENCY='Germany'", 54, &buflen, buffer); if (status != OCI_SUCCESS) /* handle error from OCINumberToText */; printf("scott's salary = %s\n", buffer); /* compare steve and scott's salaries */ status = OCINumberCmp(err, stevesal, scottsal, &result); if (status != OCI_SUCCESS) /* handle error from OCINumberCmp */; /* result is positive */ /* read jason's new salary from string */ status = OCINumberFromText(err, "48`000.00", 9, "99G999D99", 9, "NLS_NUMERIC_CHARACTERS='.`'", 27, debsal); if (status != OCI_SUCCESS) /* handle error from OCINumberFromText */; /* jason's salary is now 48000.00 */
Fixed or variable-length string data is represented to C programs as an OCIString *.
The length of the string does not include the null character.
For binding and defining variables of type OCIString * use the external typecode SQLT_VST.
See Also: The prototypes and descriptions for all the functions are provided in Chapter 17, "OCI Datatype Mapping and Manipulation Functions".
The following functions allow the C programmer to manipulate an instance of a string.
This example assigns a text string to a string, then gets a pointer to the string part of the string, as well as the string size, and prints it out.
Note the double indirection used in passing the vstring1 parameter in OCIStringAssignText().
OCIEnv *envhp; OCIError *errhp; OCIString *vstring1 = (OCIString *)0; OCIString *vstring2 = (OCIString *)0; text c_string[20]; text *text_ptr; sword status; strcpy(c_string, "hello world"); /* Assign a text string to an OCIString */ status = OCIStringAssignText(envhp, errhp, c_string, (ub4)strlen(c_string),&vstring1); /* Memory for vstring1 is allocated as part of string assignment */ status = OCIStringAssignText(envhp, errhp, "hello again", (ub4)strlen("This is a longer string."),&vstring1); /* vstring1 is automatically resized to store the longer string */ /* Get a pointer to the string part of vstring1 */ text_ptr = OCIStringPtr(envhp, vstring1); /* text_ptr now points to "hello world" */ printf("%s\n", text_ptr);
Variable-length raw data is represented in C using the OCIRaw * datatype.
For binding and defining variables of type OCIRaw *, use the external typecode SQLT_LVB.
See Also: The prototypes and descriptions for all the functions are provided in Chapter 17, "OCI Datatype Mapping and Manipulation Functions".
The following functions perform OCIRaw operations.
In this example, a raw data block is set up and a pointer to its data is obtained.
Note the double indirection in the call to OCIRawAssignBytes().
OCIEnv *envhp; OCIError *errhp; sword status; ub1 data_block[10000]; ub4 data_block_len = 10000; OCIRaw *raw1; ub1 *raw1_pointer; /* Set up the RAW */ /* assume 'data_block' has been initialized */ status = OCIRawAssignBytes(envhp, errhp, data_block, data_block_len, &raw); /* Get a pointer to the data part of the RAW */ raw1_pointer = OCIRawPtr(envhp, raw1);
Oracle provides two types of collections: variable-length arrays (varrays) and nested tables. In C applications, varrays are represented as OCIArray *, and nested tables are represented as OCITable *. Both of these datatypes (along with OCIColl and OCIIter, described later) are opaque structures.
A variety of generic collection functions enable you to manipulate collection data. You can use these functions on both varrays and nested tables. In addition, there is a set of functions specific to nested tables; see "Nested Table Manipulation Functions".
You can allocate an instance of a varray or nested table using OCIObjectNew() and free it using OCIObjectFree().
See Also: The prototypes and descriptions for all the functions are provided in Chapter 17, "OCI Datatype Mapping and Manipulation Functions".
Oracle provides two types of collections: variable-length arrays (varrays) and nested tables. Both varrays and nested tables can be viewed as sub-types of a generic collection type.
In C, a generic collection is represented as OCIColl *, a varray is represented as OCIArray *, and a nested table as OCITable *. Oracle provides a set of functions to operate on generic collections (such as OCIColl *). These functions start with the prefix OCIColl, as in OCICollGetElem(). The OCIColl*() functions can also be called to operate on varrays and nested tables.
The generic collection functions are grouped into two main categories:
The generic collection functions represent a complete set of functions for manipulating varrays. Additional functions are provided to operate specifically on nested tables. They are identified by the prefix OCITable, as in OCITableExists(). These are described in the section "Nested Table Manipulation Functions".
The following generic functions manipulate collection data:
The following generic functions enable you to scan collections with a collection iterator. The iterator is of type OCIIter, and is created by first calling OCIIterCreate().
This example creates and uses a collection iterator to scan through a varray.
OCIEnv *envhp; OCIError *errhp; text *text_ptr; sword status; OCIArray *clients; OCIString *client_elem; OCIIter *iterator; boolean eoc; dvoid *elem; OCIInd *elemind; /* Assume envhp, errhp have been initialized */ /* Assume clients points to a varray */ /* Print the elements of clients */ /* To do this, create an iterator to scan the varray */ status = OCIIterCreate(envhp, errhp, clients, &iterator); /* Get the first element of the clients varray */ printf("Clients' list:\n"); status = OCIIterNext(envhp, errhp, iterator, &elem, (dvoid **) &elemind, &eoc); while (!eoc && (status == OCI_SUCCESS)) { client_elem = *(OCIString)**elem; /* client_elem points to the string */ /* the element pointer type returned by OCIIterNext() via 'elem' is the same as that of OCICollGetElem(). Refer to OCICollGetElem() for details. */ /* client_elem points to an OCIString descriptor, so to print it out, get a pointer to where the text begins */ text_ptr = OCIStringPtr(envhp, client_elem); /* text_ptr now points to the text part of the client OCIString, which is a NULL-terminated string */ printf(" %s\n", text_ptr); status = OCIIterNext(envhp, errhp, iterator, &elem, (dvoid **)&elemind, &eoc); } if (status != OCI_SUCCESS) { /* handle error */ } /* destroy the iterator */ status = OCIIterDelete(envhp, errhp, &iterator);
As its name implies, one table may be nested or contained within another, as a variable, attribute, parameter or column. Nested tables may have elements deleted, by means of the OCITableDelete() function.
For example, suppose a table is created with 10 elements, and OCITableDelete() is used to delete elements at index 0 through 4 and 9. The first existing element is now element 5, and the last existing element is element 8.
As noted above, the generic collection functions may be used to map to and manipulate nested tables. In addition, the following functions are specific to nested tables. They should not be used on varrays.
When a nested table is fetched into the object cache, its elements are given a transient ordering, numbered from zero to the number of elements, minus 1. For example, a table with 40 elements would be numbered from 0 to 39.
You can use these position ordinals to fetch and assign the values of elements (for example, fetch to element i, or assign to element j, where i and j are valid position ordinals for the given table).
When the table is copied back to the database, its transient ordering is lost. Delete operations may be performed against elements of the table. Delete operations create transient holes; that is, they do not change the position ordinals of the remaining table elements.
In release 8.1, it is possible to retrieve a locator to a nested table. A locator is like a handle to a collection value, and it contains information about the database snapshot which exists at the time of retrieval. This snapshot information helps the database retrieve the correct instantiation of a collection value at a later time when collection elements are fetched using the locator.
Unlike a LOB locator, a collection locator cannot be used to modify a collection instance, they merely locate the correct data. Using the locator enables an application to return a handle to a nested table without having to retrieve the entire collection, which may be quite large.
A user specifies when a table is created if a locator should be returned when a collection column or attribute is fetched, using the RETURN AS LOCATOR specification.
See Also: Refer to the Oracle8i SQL Reference for more information.
You can use the OCICollIsLocator() function to determine whether a collection is a locator.
In Oracle, a REF (reference) is an identifier to an object. It is an opaque structure that uniquely locates the object. An object may point to another object by way of a REF.
In C applications, the REF is represented by OCIRef *.
See Also: The prototypes and descriptions for all the functions are provided in Chapter 17, "OCI Datatype Mapping and Manipulation Functions".
The following functions perform REF operations.
This example tests two REFs for NULL, compares them for equality, and assigns one REF to another. Note the double indirection in the call to OCIRefAssign().
OCIEnv *envhp; OCIError *errhp; sword status; boolean refs_equal; OCIRef *ref1, *ref2; /* assume refs have been initialized to point to valid objects */ /*Compare two REFs for equality */ refs_equal = OCIRefIsEqual(envhp, ref1, ref2); printf("After first OCIRefIsEqual:\n"); if(refs_equal) printf("REFs equal\n"); else printf("REFs not equal\n"); /*Assign ref1 to ref2 */ status = OCIRefAssign (envhp, errhp, ref1, &ref2); if(status != OCI_SUCCESS) /*error handling*/ /*Compare the two REFs again for equality */ refs_equal = OCIRefIsEqual(envhp, ref1, ref2); printf("After second OCIRefIsEqual:\n"); if(refs_equal) printf("REFs equal\n"); else printf("REFs not equal\n");
When a given type is created with the CREATE TYPE statement, it is stored in the server and associated with a type descriptor object (TDO). In addition, the database stores descriptor objects for each data attribute of the type, each method of the type, each parameter of each method, and the results returned by methods. The following table lists the OCI datatypes associated with each type of descriptor object.
| Information Type | OCI Datatype |
|---|---|
|
Type |
OCIType |
|
Type Attributes Collection Elements |
OCITypeElem |
|
Method |
OCITypeMethod |
Several OCI functions (including OCIBindObject() and OCIObjectNew()) require a TDO as an input parameter. An application can obtain the TDO by calling OCITypeByName(), which gets the type's TDO in an OCIType variable. Once you obtain the TDO, you can pass it, as necessary to other calls.
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