Release 9.0.1
Part Number A89860-01
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| Oracle C++ Call Interface Programmer's Guide Release 9.0.1 Part Number A89860-01 |
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This chapter is a reference for Oracle datatypes used by Oracle C++ Call Interface applications. This information will help you understand the conversions between internal and external representations of data that occur when you transfer data between your application and the database server.
This chapter includes the following topics:
Accurate communication between your C++ program and the Oracle database server is critical. OCCI applications can retrieve data from database tables by using SQL queries or they can modify existing data through the use of SQL INSERT, UPDATE, and DELETE functions. To facilitate communication between the host language C++ and the database server, you must be aware of how C++ datatypes are converted to Oracle datatypes and back again.
In the Oracle database, values are stored in columns in tables. Internally, Oracle represents data in particular formats called internal datatypes. NUMBER, VARCHAR2, and DATE are examples of Oracle internal datatypes.
OCCI applications work with host language datatypes, or external datatypes, predefined by the host language. When data is transferred between an OCCI application and the database server, the data from the database is converted from internal datatypes to external datatypes.
OCCI defines an enumerator called Type that lists the possible data representation formats available in an OCCI application. These representation formats are called external datatypes. When data is sent to the database server from the OCCI application, the external datatype indicates to the database server what format to expect the data. When data is requested from the database server by the OCCI application, the external datatype indicates the format of the data to be returned.
For example, on retrieving a value from a NUMBER column, the program may be set to retrieve it in OCCIINT format (a signed integer format into an integer variable). Or, the client might be set to send data in OCCIFLOAT format (floating-point format) stored in a C++ float variable to be inserted in a column of NUMBER type.
An OCCI application binds input parameters to a Statement, by calling a setxxx method (the external datatype is implicitly specified by the method name), or by calling the registerOutParam, setDataBuffer, or setDataBufferArray method (the external datatype is explicitly specified in the method call). Similarly, when data values are fetched through a ResultSet object, the external representation of the retrieved data must be specified. This is done by calling a getxxx method (the external datatype is implicitly specified by the method name) or by calling the setDataBuffer method (the external datatype is explicitly specified in the method call).
The internal (built-in) datatypes provided by Oracle are listed in this section.
Table 4-1 lists the Oracle internal datatypes and maximum internal length of each:
You can use five Oracle internal datatypes to specify columns that contain either characters or arrays of bytes: CHAR, VARCHAR2, RAW, LONG, and LONG RAW.
CHAR, VARCHAR2, and LONG columns normally hold character data. RAW and LONG RAW hold bytes that are not interpreted as characters, for example, pixel values in a bitmapped graphics image. Character data can be transformed when passed through a gateway between networks. For example, character data passed between machines by using different languages (where single characters may be represented by differing numbers of bytes) can be significantly changed in length. Raw data is never converted in this way.
The database designer is responsible for choosing the appropriate Oracle internal datatype for each column in a table. You must be aware of the many possible ways that character and byte-array data can be represented and converted between variables in the OCCI program and Oracle database tables.
The universal rowid (UROWID) is a datatype that can store both the logical and the physical rowid of rows in Oracle tables and in foreign tables, such as DB2 tables accessed through a gateway. Logical rowid values are primary key-based logical identifiers for the rows of index organized tables.
To use columns of the UROWID datatype, the value of the COMPATIBLE initialization parameter must be set to 8.1 or higher.
The following OCCI_SQLT types can be bound to universal rowids:
OCCI_SQLT_CHR (VARCHAR2)
OCCI_SQLT_VCS (VARCHAR)
OCCI_SQLT_STR (null terminated string)
OCCI_SQLT_LVC (long VARCHAR)
OCCI_SQLT_AFC (CHAR)
OCCI_SQLT_AVC (CHARZ)
OCCI_SQLT_VST (string)
OCCI_SQLT_RDD (ROWID descriptor)
Communication between the host OCCI application and the Oracle database server is through the use of external datatypes. Specifically, external datatypes are mapped to C++ datatypes.
Table 4-2 lists the Oracle external datatypes, the C++ equivalent (what the Oracle internal datatype is usually converted to), and the corresponding OCCI type:
| External Datatype | Code | C++ Datatype | OCCI Type |
|---|---|---|---|
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Binary |
114 |
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Binary |
113 |
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96 |
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Character |
112 |
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97 |
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12 |
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4 |
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16 bit signed |
3 |
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32 bit signed |
3 |
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8 bit signed |
3 |
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190 |
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189 |
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8 |
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24 |
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94 |
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95 |
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108 |
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2 |
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23 |
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110 |
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11 |
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104 |
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null-terminated |
5 |
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187 |
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232 |
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188 |
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68 |
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9 |
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1 |
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6 |
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15 |
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Most of the following external datatypes are represented as C++ classes in OCCI. Please refer to Chapter 8, "OCCI Classes and Methods" for additional information. |
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IntervalDS |
OCCIINTERVALDS |
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IntervalYM |
OCCIINTERVALYM |
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Please note the usage of the types in the following methods of the Statement class:
registerOutParam: Only types of the form OCCIxxx (for example, OCCIDOUBLE, OCCICURSOR, and so on) on the occiCommon.h file are permitted. However, there are some exceptions. OCCIANYDATA, OCCIMETADATA, OCCISTREAM, and OCCIBOOL are not permitted.
setDataBuffer() and setDataBufferArray: Only types of the form OCCI_SQLT_xxx (for example, OCCI_SQLT_INT) in the occiCommon.h file are permitted.
Please note the usage of the types in the following methods of the ResultSet class:
setDataBuffer() and setDataBufferArray: Only types of the form OCCI_SQLT_xxx (for example, OCCI_SQLT_INT) in the occiCommon.h file are permitted.
This section provides a description for each of the external datatypes.
The external datatype BFILE allows read-only byte stream access to large files on the file system of the database server. A BFILE is a large binary data object stored in operating system files outside database tablespaces. These files use reference semantics. The Oracle server can access a BFILE provided the underlying server operating system supports stream-mode access to these operating system files.
The external datatype BLOB stores unstructured binary large objects. A BLOB can be thought of as a bitstream with no character set semantics. BLOBs can store up to 4 gigabytes of binary data.
BLOB datatypes have full transactional support. Changes made through OCCI participate fully in the transaction. BLOB value manipulations can be committed or rolled back. You cannot save a BLOB locator in a variable in one transaction and then use it in another transaction or session.
The external datatype CHAR is a string of characters, with a maximum length of 2000 characters. Character strings are compared by using blank-padded comparison semantics.
The external datatype CHARZ is similar to the CHAR datatype, except that the string must be null terminated on input, and Oracle places a null terminator character at the end of the string on output. The null terminator serves only to delimit the string on input or output. It is not part of the data in the table.
The external datatype CLOB stores fixed-width or varying-width character data. A CLOB can store up to 4 gigabytes of character data. CLOBs have full transactional support. Changes made through OCCI participate fully in the transaction. CLOB value manipulations can be committed or rolled back. You cannot save a CLOB locator in a variable in one transaction and then use it in another transaction or session.
The external datatype DATE can update, insert, or retrieve a date value using the Oracle internal date binary format, which contains seven bytes, as listed in Table 4-3:
| Byte 1 | Byte 2 | Byte 3 | Byte 4 | Byte 5 | Byte 6 | Byte 7 | |
|---|---|---|---|---|---|---|---|
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Meaning: |
Century |
Year |
Month |
Day |
Hour |
Minute |
Second |
|
Example (01-JUN-2000, 3:17PM): |
120 |
100 |
6 |
1 |
16 |
18 |
1 |
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Example (01-JAN-4712 BCE): |
53 |
88 |
1 |
1 |
1 |
1 |
1 |
The century and year bytes (1 and 2) are in excess-100 notation. Dates BCE (Before Common Era) are less than 100. Dates in the Common Era, 0 and after, are greater than 100. For dates 0 and after, the first digit of both bytes 1 and 2 merely signifies that it is of the Common Era.
For byte 1, the second and third digits of the century are calculated as the year (an integer) divided by 100. With integer division, the fractional portion is discarded. The following calculation is for the year 1992:
1992 / 100 = 19
For byte 1, 119 represents the twentieth century, 1900 to 1999. A value of 120 would represent the twenty-first century, 2000 to 2099.
For byte 2, the second and third digits of the year are calculated as the year modulo 100. With a modulo division, the nonfractional portion is discarded:
1992 % 100 = 92
For byte 2, 192 represents the ninety-second year of the current century. A value of 100 would represent the zeroth year of the current century.
The year 2000 would yield 120 for byte 1 and 100 for byte 2.
For years prior to 0 CE, centuries and years are represented by the difference between 100 and the number. So 01-JAN-4712 BCE is century 53 because 100 - 47 = 53. The year is 88 because the 100 - 12 = 88.
Valid dates begin at 01-JAN-4712 BCE. The month byte ranges from 1 to 31, the hour byte ranges from 1 to 24, and the second byte ranges from 1 to 60.
When you enter a date in binary format by using the external datatype DATE, the database does not perform consistency or range checking. All data in this format must be validated before input.
When a DATE column is converted to a character string in your program, it is returned in the default format mask for your session, or as specified in the INIT.ORA file.
Note that this datatype is different from OCCI DATE which corresponds to a C++ Date datatype.
The external datatype FLOAT processes numbers with fractional parts. The number is represented in the host system's floating-point format. Normally, the length is 4 or 8 bytes.
The internal format of an Oracle number is decimal. Most floating-point implementations are binary. Oracle, therefore, represents numbers with greater precision than floating-point representations.
The external datatype INTEGER is used for converting numbers. An external integer is a signed binary number. Its size is operating system-dependent. If the number being returned from Oracle is not an integer, then the fractional part is discarded, and no error is returned. If the number returned exceeds the capacity of a signed integer for the system, then Oracle returns an overflow on conversion error.
The external datatype INTERVAL DAY TO SECOND stores the difference between two datetime values in terms of days, hours, minutes, and seconds. Specify this datatype as follows:
INTERVAL DAY [(day_precision)] TO SECOND [(fractional_seconds_precision)]
This example uses the following placeholders:
DAY datetime field. Accepted values are 1 to 9. The default is 2.
fractional_seconds_precision: Number of digits in the fractional part of the SECOND datetime field. Accepted values are 0 to 9. The default is 6.
To specify an INTERVAL DAY TO SECOND literal with nondefault day and second precisions, you must specify the precisions in the literal. For example, you might specify an interval of 100 days, 10 hours, 20 minutes, 42 seconds, and 22 hundredths of a second as follows:
INTERVAL '100 10:20:42.22' DAY(3) TO SECOND(2)
You can also use abbreviated forms of the INTERVAL DAY TO SECOND literal. For example:
The external datatype INTERVAL YEAR TO MONTH stores the difference between two datetime values by using the YEAR and MONTH datetime fields. Specify INTERVAL YEAR TO MONTH as follows:
INTERVAL YEAR [(year_precision)] TO MONTH
The placeholder year_precision is the number of digits in the YEAR datetime field. The default value of year_precision is 2. To specify an INTERVAL YEAR TO MONTH literal with a nondefault year_precision, you must specify the precision in the literal. For example, the following INTERVAL YEAR TO MONTH literal indicates an interval of 123 years, 2 months:
INTERVAL '123-2' YEAR(3) TO MONTH
You can also use abbreviated forms of the INTERVAL YEAR TO MONTH literal. For ex
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The external datatype LONG stores character strings longer than 4000 bytes and up to 2 gigabytes in a column of datatype LONG. Columns of this type are only used for storage and retrieval of long strings. They cannot be used in methods, expressions, or WHERE clauses. LONG column values are generally converted to and from character strings.
The external datatype LONG RAW is similar to the external datatype RAW, except that it stores up to 2 gigabytes.
The external datatype LONG VARCHAR stores data from and into an Oracle LONG column. The first four bytes contain the length of the item. The maximum length of a LONG VARCHAR is 2 gigabytes.
The external datatype LONG VARRAW store data from and into an Oracle LONG RAW column. The length is contained in the first four bytes. The maximum length is 2 gigabytes.
The external datatype NCLOB is a national character version of a CLOB. It stores fixed-width, multibyte national character set character (NCHAR), or varying-width character set data. An NCLOB can store up to 4 gigabytes of character text data.
NCLOBs have full transactional support. Changes made through OCCI participate fully in the transaction. NCLOB value manipulations can be committed or rolled back. You cannot save an NCLOB locator in a variable in one transaction and then use it in another transaction or session.
You cannot create an object with NCLOB attributes, but you can specify NCLOB parameters in methods.
You should not need to use NUMBER as an external datatype. If you do use it, Oracle returns numeric values in its internal 21-byte binary format and will expect this format on input. The following discussion is included for completeness only.
Oracle stores values of the NUMBER datatype in a variable-length format. The first byte is the exponent and is followed by 1 to 20 mantissa bytes. The high-order bit of the exponent byte is the sign bit; it is set for positive numbers and it is cleared for negative numbers. The lower 7 bits represent the exponent, which is a base-100 digit with an offset of 65.
To calculate the decimal exponent, add 65 to the base-100 exponent and add another 128 if the number is positive. If the number is negative, you do the same, but subsequently the bits are inverted. For example, -5 has a base-100 exponent = 62 (0x3e). The decimal exponent is thus (~0x3e) -128 - 65 = 0xc1 -128 -65 = 193 -128 -65 = 0.
Each mantissa byte is a base-100 digit, in the range 1 to 100. For positive numbers, the digit has 1 added to it. So, the mantissa digit for the value 5 is 6. For negative numbers, instead of adding 1, the digit is subtracted from 101. So, the mantissa digit for the number -5 is 96 (101 - 5). Negative numbers have a byte containing 102 appended to the data bytes. However, negative numbers that have 20 mantissa bytes do not have the trailing 102 byte. Because the mantissa digits are stored in base-100, each byte can represent two decimal digits. The mantissa is normalized; leading zeroes are not stored.
Up to 20 data bytes can represent the mantissa. However, only 19 are guaranteed to be accurate. The 19 data bytes, each representing a base-100 digit, yield a maximum precision of 38 digits for an internal datatype NUMBER.
Note that this datatype is different from OCCI NUMBER which corresponds to a C++ Number datatype.
The external datatype OCCI STRING corresponds to an STL string.
The external datatype OCCI VECTOR is used to represent collections, for example, a nested table or VARRAY. CREATE TYPE num_type as VARRAY OF NUMBER(10) can be represented in a C++ application as vector<int>, vector<Number>, and so on.
The external datatype RAW is used for binary data or byte strings that are not to be interpreted or processed by Oracle. RAW could be used, for example, for graphics character sequences. The maximum length of a RAW column is 2000 bytes.
When RAW data in an Oracle table is converted to a character string, the data is represented in hexadecimal code. Each byte of RAW data is represented as two characters that indicate the value of the byte, ranging from 00 to FF. If you input a character string by using RAW, then you must use hexadecimal coding.
The external datatype REF is a reference to a named datatype. To allocate a REF for use in an application, declare a variable as a pointer to a REF.
The external datatype ROWID identifies a particular row in a database table. The ROWID is often returned from a query by issuing a statement similar to the following example:
SELECT ROWID, var1, var2 FROM db
You can then use the returned ROWID in further DELETE statements.
If you are performing a SELECT for an UPDATE operation, then the ROWID is implicitly returned.
The external datatype STRING behaves like the external datatype VARCHAR2 (datatype code 1), except that the external datatype STRING must be null-terminated.
Note that this datatype is different from OCCI STRING which corresponds to a C++ STL string datatype.
The external datatype TIMESTAMP is an extension of the DATE datatype. It stores the year, month, and day of the DATE datatype, plus hour, minute, and second values. Specify the TIMESTAMP datatype as follows:
TIMESTAMP [(fractional_seconds_precision)]
The placeholder fractional_seconds_precision optionally specifies the number of digits in the fractional part of the SECOND datetime field and can be a number in the range 0 to 9. The default is 6. For example, you specify TIMESTAMP(2) as a literal as follows:
TIMESTAMP '1997-01-31 09:26:50.10'
Note that this datatype is different from OCCI TIMESTAMP.
The external datatype TIMESTAMP WITH TIME ZONE (TSTZ) is a variant of TIMESTAMP that includes an explicit time zone displacement in its value. The time zone displacement is the difference (in hours and minutes) between local time and UTC (Coordinated Universal Time--formerly Greenwich Mean Time). Specify the TIMESTAMP WITH TIME ZONE datatype as follows:
TIMESTAMP(fractional_seconds_precision) WITH TIME ZONE
The placeholder fractional_seconds_precision optionally specifies the number of digits in the fractional part of the SECOND datetime field and can be a number in the range 0 to 9. The default is 6.
Two TIMESTAMP WITH TIME ZONE values are considered identical if they represent the same instant in UTC, regardless of the TIME ZONE offsets stored in the data.
The external datatype TIMESTAMP WITH TIME ZONE is a variant of TIMESTAMP that includes a time zone displacement in its value. The time zone displacement is the difference (in hours and minutes) between local time and UTC (Coordinated Universal Time--formerly Greenwich Mean Time). Specify the TIMESTAMP WITH TIME ZONE datatype as follows:
TIMESTAMP [(fractional_seconds_precision)] WITH TIME ZONE
The placeholder fractional_seconds_precision optionally specifies the number of digits in the fractional part of the SECOND datetime field and can be a number in the range 0 to 9. The default is 6. For example, you might specify TIMESTAMP(0) WITH TIME ZONE as a literal as follows:
TIMESTAMP '1997-01-31 09:26:50+02.00'
The external datatype UNSIGNED INT is used for unsigned binary integers. The size in bytes is operating system dependent. The host system architecture determines the order of the bytes in a word. If the number being output from Oracle is not an integer, the fractional part is discarded, and no error is returned. If the number to be returned exceeds the capacity of an unsigned integer for the operating system, Oracle returns an overflow on conversion error.
The external datatype VARCHAR store character strings of varying length. The first two bytes contain the length of the character string, and the remaining bytes contain the actual string. The specified length of the string in a bind or a define call must include the two length bytes, meaning the largest VARCHAR string is 65533 bytes long, not 65535. For converting longer strings, use the LONG VARCHAR external datatype.
The external datatype VARCHAR2 is a variable-length string of characters up to 4000 bytes.
The external datatype VARNUM is similar to the external datatype NUMBER, except that the first byte contains the length of the number representation. This length value does not include the length byte itself. Reserve 22 bytes to receive the longest possible VARNUM. You must set the length byte when you send a VARNUM value to the database.
The external datatype VARRAW is similar to the external datatype RAW, except that the first two bytes contain the length of the data. The specified length of the string in a bind or a define call must include the two length bytes. So the largest VARRAW string that can be received or sent is 65533 bytes, not 65535. For converting longer strings, use the LONG VARRAW datatype.
Table 4-5 lists the supported conversions from Oracle internal datatypes to external datatypes, and from external datatypes to internal column representations. Note the following conditions:
REF stored in the database is converted to OCCI_SQLT_REF on output
OCCI_SQLT_REF is converted to the internal representation of a REF on input
OCCI_SQLT_NTY (and represented by a C structure in the application) on output
OCCI_SQLT_NTY (represented by a C structure in an application) is converted to the internal representation of the corresponding datatype on input
LOB and a BFILE are represented by descriptors in OCCI applications, so there are no input or output conversions
| INTERNAL DATATYPES | ||
|---|---|---|
| EXTERNAL DATATYPES | CLOB | BLOB |
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I/O |
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I/O |
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I/O |
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I/O |
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I/O |
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I/O |
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I/O |
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I/O |
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I/O |
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I/O |
You can also use one of the character data types for the host variable used in a fetch or insert operation from or to a datetime or interval column. Oracle will do the conversion between the character data type and datetime/interval data type for you.
TSLTZ to CHAR, DATE, TIMESTAMP and TSTZ, the value will be adjusted to the session time zone.
CHAR, DATE, and TIMESTAMP to TSLTZ, the session time zone will be stored in memory.
TSLTZ to ANSI DATE, the time portion will be zero.
TSTZ, the time zone which the time stamp is in will be stored in memory.
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 Copyright © 1996-2001, Oracle Corporation. All Rights Reserved. |
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