From bfa452a375ea0a0a3f95304a69186936567e5263 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?J=C3=B6rg=20Frings-F=C3=BCrst?= Date: Mon, 14 Aug 2023 19:45:36 +0200 Subject: New upstream version 4.1.4 --- docs/html/xbc4.html | 81 ----------------------------------------------------- 1 file changed, 81 deletions(-) delete mode 100755 docs/html/xbc4.html (limited to 'docs/html/xbc4.html') diff --git a/docs/html/xbc4.html b/docs/html/xbc4.html deleted file mode 100755 index a0275ed..0000000 --- a/docs/html/xbc4.html +++ /dev/null @@ -1,81 +0,0 @@ - - -Xbase DBMS Chapter 4 - -

Date Processing

Chapter Updated 12/09/22

- -The objective of this chapter is to provide information regarding -the basic concepts of date arithmetic and supply generic -C/C++ date methods.

- -

Leap Years

- -Due to the fact that it actually takes about 365 1/4 days for -the earth to circle the sun, every fourth year and every fourth -century have an extra day added to the end of February and the year -is called a leap year. Leap years have 366 days, non leap years -have 365 days. The following code segment describes how to -determine if a given year is a leap year. - -A leap year is a year having 366 days, which can be evenly -divisible by 4 and not by 100 or divisible by 400. - -There are also leap centuries. Leap centuries are years which -are evenly divisible by 400. - -To calculate a leap year, the following code segment can be used - - - int year; - - if(( year % 4 == 0 && year % 100 != 0 ) || year % 400 = 0 ) - LEAP_YEAR = TRUE; - else - LEAP_YEAR = FALSE - - - -

Julian Dates

- -Around the time of Jesus Christ, a fellow with the name of Julias Ceasar -established the Julian calendar. The Julian calendar established every -fourth year as a leap year with 366 days and all other years having 365 days. -The months were set up the same as they are with a Gregorian calendar, which -is what we use today. A Julian date is defined as as the number of days from the -first day of the year; February 1 would have a Julian day of 32.

- -From a programmer's perspective, Julian dates are useful for doing date -arithmetic, determining the difference between two dates or calculating -a future or past date.

- -To determine the difference between two dates, convert both dates to a -Julian date and subtract one from the other.

- -To calculate a future or past date, convert the base date to a Julian date, -add (or subtract) the number of days necessary to (from) it and convert the -julian date back to a Gregorian date.

- -The Julian date routines use a base date of 01/01/0001. DBase julian Dates have an offset of 1721425L, reason unknown. -

- -

Gregorian Dates

- -In 1582, Pope Gregor XIII introduced a corrected form of the Julian calendar. -Every 4th year still has 366 days except for century years. Century years -were added as leap years if evenly divisible by 400. The year 2000 is a leap century. -

- -The methods supplied with this software are based on gregorian dates with -the format of CCYYMMDD for century, year, month and day.

- - -

Date Formats

- -All dates are stored in the .DBF files with format CCYYMMDD.

-All date routines work with dates formated with the same CCYYMMDD format.

- -

- - -- cgit v1.2.3 From c894a7cdd8686ea695602a23a511a3f1b0d047be Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?J=C3=B6rg=20Frings-F=C3=BCrst?= Date: Mon, 14 Aug 2023 21:07:46 +0200 Subject: New upstream version 4.1.4 --- docs/html/xbc4.html | 208 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 208 insertions(+) create mode 100755 docs/html/xbc4.html (limited to 'docs/html/xbc4.html') diff --git a/docs/html/xbc4.html b/docs/html/xbc4.html new file mode 100755 index 0000000..f8a48d9 --- /dev/null +++ b/docs/html/xbc4.html @@ -0,0 +1,208 @@ + + +Xbase DBMS Chapter 4 + +

Expression Handling

Chapter Updated 04/28/23

+ +

Overview

+ +The main objective of this chapter is to provide information regarding the +basic concepts of using the Xbase64 Expression module.

+ +The Xbase64 library includes an expression parsing routine which assists +application programmers by providing a high level data manipulation tool and +also allows for building complex index keys. + +The functions included were derived from dBASE III Plus, dBASE IV and Clipper. +

+Expressions are primarily used for index key definitions and filter criteria, but +can also be used for other tasks as well. +

+ +

Internal fuctioning

+The expression module works in two phases. Firstly, method +ParseExpression is called and builds an expression tree from +all the components of the expression. The tree is made up of individual +nodes. The expression is checked for valid field names, literals, +operands and functions. Any field references are resolved. If fields +are used in an expression and the database name for the field is not +included in the name with the -> operand, the routines assume the +associated database has been successfully opened. +

+Secondly, method ProcessExpression is called to process the +expression tree created by ParseExpression(). The routine parses each +node in the expression tree, executing functions, processing operands +and manipulating data to produce the desired result.

+ +If an expression will be processed repeatedly, it is best to pre-parse the +tree using ParseExpression, then for each new call to the expression, +execute method ProcessExpression which processes the tree. + +

Expression Return Types

+Expressions will return a type of CHAR, NUMERIC, DATE or LOGICAL.

+ +An expression return type can be determined with method +GetExpressionResultType after parsing it.

+ +Expressions returning a return type of CHAR are limited to a 200 byte internal +buffer. There is also a 100 byte limit for NDX and MDX index key support. If +the 200 byte limit is not large enough for your application, adjust field +enum { WorkBufMaxLen = 200 }; in file exp.h. + +

+ + + + + + +

Return Type	XBase Type
CHAR	xbString
NUMERIC	xbDouble
DATE	xbDate
LOGICAL	xbBool

+ +

+Date routines return an xbDate result. In addition, the date value can be +extracted using GetStringResult() which returns YYYYMMDD or GetDoubleResult() +which returns a julian value. + +

+

Expression Functions

+Each expression function also has a corresponding C++ function. It is +slightly more efficient to call the C++ functions directly, rather than +execute the expression parsing routines.

+ +To add a new function, find a function that is similar to what you need, copy +the code and modify xbxbase.h, xbfuncs.cpp, xbexp.cpp and xb_test_expression.cpp.

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +

Function Name	Return Type	Description
ABS	N	Calculate absolute value of numeric expression
ALLTRIM	C	Trim leading andtrailing whitespace from a string
ASC	N	Return ASCII code for first character in a string
AT	N	Return starting position of a string within a string
CDOW	C	Retun character weekday name for a date
CHR	C	Convert numeric expression to a character
CMONTH	C	Return month name for a date
CTOD	D	Return date from a character date input
DATE	D	Return system date
DAY	N	Return the day of the month from a date
DEL	C	Return record deletion status for a record
DELETED	L	Return record deletion status for a record<
DESCEND	1	Clipper DESCEND function
DOW	N	Return number of day of week
DTOC	C	Return character date from input date
DTOS	C	Return character CCYYMMDD date from input date
EXP	N	Return exponent value
IIF	C	Immediate If
INT	N	Convert number to integer, truncate any decimals
ISALPHA	L	Check if string begins with alpha character
ISLOWER	L	Check if string begins with lower case alpha character
ISUPPER	L	Check if string begins with upper case character
LEFT	C	Return left characters from a string
LEN	N	Return lenght of string
LOG	N	Calculate logarithm
LOWER	C	Convert upper case to lower case
LTRIM	C	Trim left side of a string
MAX	N	Return higher of two values
MIN	N	Return lesser of two values
MONTH	N	Return number of month for a given date
RECNO	N	Return current rec number for a given table
RECCOUNT	N	Return number of records in a given table
REPLICATE	C	Repeat character expression N times
RIGHT	C	Return right characters from as tring
RTRIM	C	Trim right side of string
SPACE	C	Generate a string of N spaces
SQRT	N	Calculate square root
STOD	D	Convert 8 byte CCYYMMDD date to date
STR	C	Convert number to character string
STRZERO	C	Convert number to character string with leading zeroes. Clipper Function.
SUBSTR	C	Extract portion oif one string from another string
TRIM	C	Trim left and right sides of a string
UPPER	C	Conver lower case to upper case
VAL	N	Convert numeric characters to number
YEAR	N	Return year for a given date

+ +

+

Expression Components

+Expressions are made up of one or more tokens. A token is one of literal, +database field, operand or function. Literals are either numeric or character. +Character literals are enclosed in 'single' or "double" quotes. numeric +literals are a series of one or more contiguous numerals, ".", "+" or "-'". +

+A field is simply a field name in the default database, or is in the form +of database->fieldname. + + +

+

Expression Literals

+ + + + + + +

Type	Example
CHAR	"literal" or 'literal'
NUMERIC	+99999.99
DATE	{10/07/60} or {02/09/1989}

+ +

+

Expression Operators

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +

Type	Operator	Precedence	Result	Notes
Parens	()	12
Numeric Operator	+ (unary)	11	N
Numeric Operator	- (unary)	11	N
Numeric Operator	--X	10	N
Numeric Operator	++X	10	N
Numeric Operator	**	9	N
Numeric Operator	^	9	N
Numeric Operator	%	8	N
Numeric Operator	*	8	N
Numeric Operator	/	8	N
Numeric Operator	+ Addition	7	N
Numeric Operator	- Subtraction	7	N
Numeric Operator	X--	6	N
Numeric Operator	X++	6	N
String Operator	+	5	C	Concatonate 1
String Operator	-	5	C	Concatonate 2
Relational Operator	=	4	L	N,C,D
Relational Operator	#, <>, !=	4	N,C,D
Relational Operator	<	4	L	N,C,D
Relational Operator	>	4	L	N,C,D
Relational Operator	<=	4	L	N,C,D
Relational Operator	>=	4	L	N,C,D
Relational Operator	$	4	L	N,C,D
Relational Operator	==			Clipper operator, not implemented yet
Logical Operator	NOT	3	L	Evaluated after all math and relational operators
Logical Operator	.NOT.	3	L	Evaluated after all math and relational operators
Logical Operator	AND	2	L	Evaluated after all math and relational operators
Logical Operator	.AND.	2	L	Evaluated after all math and relational operators
Logical Operator	OR	1	L	Evaluated after all math and relational operators
Logical Operator	.OR.	1	L	Evaluated after all math and relational operators

+ +

+

Example Expressions

CUSTOMERS->LNAME + ", " + CUSTOMERS->FNAME +

LNAME + ", " + FNAME +

STARTDT + 90 +

DATE() - 7 +

YEAR( TODAY() ) +

IIF( "A" = "N", "true result", "false result" ) +

IIF( "A" = "N" .OR. 2 > 1 , "true result", "false result" ) +

IIF( .NOT. "A" = "N", "true result", "false result" ) +

.NOT. DELETED() +

+ + +

Example program

+For an example on how to use the expression logic, see program +src/examples/xb_ex_expression.cpp. +

+ +

+ + -- cgit v1.2.3