BCD and currency types in Delphi

DelphiMediumBCDAndCurrencyType

 I.BCDType

BCD is binary-coded decimal type. in Delphi, the BCD field type can accurately store the floating point data type.

The data type of the BCD code supported by Delphi is tbcd. Its definition is as follows:

Tbcd = packed record Precision: byte; {1 .. 64} Signspecialplaces: byte; {sign: 1, Special: 1, places: 6} Fraction: packed array [0 .. 31] of byte; {BCD nibbles, 00 .. 99 per byte, high nibble 1st} End;

BCD is supported in the fmtbcd unit. Therefore, to use the BCD function, you must reference this unit.

The BCD functions of Delphi include:

Bcdadd	Calculate the sum of two BCD codes
Bcdcompare	Compare the two BCD sizes
Bcddivide	Division of BCD data
Bcdmultiply	BCD data Multiplication
Bcdprecision	Returns the number of BCD data records. For example, if BCD 123 returns 3, and BCD 9382 returns 4.
Bcdscale	Returns the decimal places of BCD codes.
Bcdsubtract	Subtract Two BCD codes
Bcdtocurr	Convert BCD code to current data type
Bcdtodouble	Data Type converted from BCD to double
Bcdtointeger	Data Type converted from BCD to integer
Bcdtostr	BCD code to a string
Bcdtostrf	Convert BCD code to a string with format Control
Currtobcd	Current data type conversion to BCD code
Doubletobcd	Convert double data type to BCD code
Formatbcd	Format the BCD code as a string
Integertobcd	Convert Integer type to BCD code
Isbcdnegative	Determine whether BCD is negative
Normalizebcd	Converts a BCD value to another BCD value based on the given precision and decimal places.
Nullbcd	Determine whether BCD is null
Strtobcd	Convert string to BCD code
Trystrtobcd	If the string is converted to a BCD code, the default value is returned if the conversion fails.

 II.CurrencyType

The same as the money type in SQL Server, the currency type in Delphi:

1) occupies 8 bytes.

2) always four decimal places.

3) range:-2 ^ 63 ~ 2 ^ 63-1 (-922,337,203,685,477.5808 ~ 922,337,203,685,477.5807 ). The storage format is always multiplied by 10000, and then saved in integer format.

 III.BCDField Type (Tbcdfield)

Currently, many databases have decimal and numeric data types. They can precisely store floating point data and map decimal and numeric data types to BCD fields.

In the tdatabase control of BDE, there is an enablebcd option:

The enablebcd option is also available in ADO tadoquery.

 

 

The enablebcd option describes how to process numeric fields (decimal and numeric:

1) When enablebcd is true, the field ing of the numerical type is a tbcdfield class.

2) When enablebcd is set to false, the numeric field is mapped to the tfloatfield class.

Tbcdfield is defined in the DB. Pas file:

Tbcdfield = Class (tnumericfield) Private Fcurrency: Boolean; Fcheckrange: Boolean; Fminvalue: currency; Fmaxvalue: currency; Fpretries: integer; Procedure setcurrency (value: Boolean ); Procedure setmaxvalue (value: currency ); Procedure setminvalue (value: currency ); Procedure setprecision (value: integer ); Procedure updatecheckrange; Protected Class procedure checktypesize (value: integer); override; Procedure copydata (source, DEST: pointer); override; Function getasbcd: tbcd; override; Function getascurrency: currency; override; Function getasfloat: Double; override; Function getasinteger: longint; override; Function getasstring: string; override; Function getasvariant: variant; override; Function getdatasize: integer; override; Function getdefaultwidth: integer; override; Procedure gettext (VAR text: string; displaytext: Boolean); override; Function getvalue (VaR value: currency): Boolean; Procedure setasbcd (const value: tbcd); override; Procedure setascurrency (value: currency); override; Procedure setasfloat (value: Double); override; Procedure setasinteger (value: longint); override; Procedure setasstring (const value: string); override; Procedure setvarvalue (const value: variant); override; Public Constructor create (aowner: tcomponent); override; Property Value: currency read getascurrency write setascurrency; Published {Lowercase to avoid name clash with C ++ currency type} Property currency: Boolean read fcurrency write setcurrency default false; Property maxvalue: currency read fmaxvalue write setmaxvalue; Property minvalue: currency read fminvalue write setminvalue; Property precision: integer read fpresponwrite setprecision default 0; Property size default 4; End;

Because tbcdfield uses the currency type to store data (Note: It is not stored using tbcd), and currency is fixed with only four decimal places, therefore, if the precision exceeds 4 bits, use tfloatfield (enablebcd BIT false ).

4.References

1. Direct support for BCD codes in Delphi.

Http://www.cnblogs.com/ywangzi/archive/2012/11/14/2769823.html

 

BCD and currency types in Delphi