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Poll
How big is your Baan-DB (just Data AND Indexes)
0 - 200 GB
15%
200 - 500 GB
30%
500 - 800 GB
4%
800 - 1200 GB
4%
1200 - 1500 GB
11%
1500 - 2000 GB
15%
> 2000 GB
22%
Total votes: 27

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Flow of 4GL engine
By patvdv at 26 Feb 2008 - 21:56


Flow of 4GL engine

This section presents the general flow of the 4GL engine. It is not complete, but the most important actions are included. The flow is similar for programs of types 1, 2, 3, and 4. Any differences are indicated by comments.

Main routine

The main routine displays the first form on the screen and waits for a command.

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Declarations
By patvdv at 26 Feb 2008 - 21:56

Declarations

You can declare variables either within a function block or at the start of the program. Variables declared in a function block can be used within that function block only. Variables declared at the start of the program can be used in each function described below the declaration.

General syntax

You declare variables with the following syntax (parts between [ ] are optional):

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Long expressions (ON CASE)
By patvdv at 26 Feb 2008 - 21:56


Long expressions (ON CASE)

The expression after ON CASE is evaluated and compared with the various CASE expressions that follow. All expressions in the case labels must be of type LONG or STRING. When string expressions are used, the ASCII value of the string is compared with the ON CASE expression. For example:

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Domains
By patvdv at 26 Feb 2008 - 21:56

Domains

When declaring temporary variables for storing values of database fields, you can use normal variables of type long, double, or string. But this can cause problems if the length or type of the table field has been changed in the data dictionary. It is preferable to use domain declarations for storing the value of a database table field. When you use a domain declaration, the type and length for the declared variable are read from the data dictionary.

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Macro definition (preprocessor)
By patvdv at 26 Feb 2008 - 21:56

Macro definition (preprocessor)

Use the following statement to define a macro:

#define macroname[(arguments)]

Use the folowing statement to undefine a macro:

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Enumerate and set constants
By patvdv at 26 Feb 2008 - 21:56


Enumerate and set constants

In the data dictionary you can define database table fields and domains of type enumerate or set.

An enumerate or set domain consists of a number of constants. In the program script (and other places in the data dictionary), a symbolic name is used. The symbolic name is the domain name, followed by a period [.] followed by the name of the constant. Variables of type set can also consist of a combination of set values.

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Multibyte strings
By patvdv at 26 Feb 2008 - 21:56

Multibyte strings

A string variable can be declared as a multibyte string, in order to handle multibyte or bidirectional characters. For example:

STRING mb_str(10,5) MB | 5 multibyte strings of 10 characters

In a single-byte string, each byte contains a single character. But in a multibyte string, characters can occupy from one to four bytes.

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Expressions and operators
By patvdv at 26 Feb 2008 - 21:56

Expressions and operators

An expression is a combination of variables, constants, and operators, built up in accordance with certain rules. There are two main kinds of operators: unary and binary. All operators, except the negation operators, are binary. Expressions with unary operators have the general form:

operator operand

Expressions with binary operators have the following form, where each operand can be another expression, variable, or constant:

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NULL characters in strings
By patvdv at 26 Feb 2008 - 21:56


NULL characters in strings

Technically, a string is an array of characters. The internal representation of a string has a NULL character [] at the end. The NULL character represents the character with the value zero.

Null characters can occur within strings after use of the following functions:

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External variables
By patvdv at 26 Feb 2008 - 21:56

External variables

An external variable is declared outside the function blocks. You can use them in all functions that occur after the variable declaration, and also in other programs (for example, forms, reports, and runtime expressions). It is possible to declare external variables within a function block but this is not recommended.
If a local variable has the same name as an external variable, the local variable is used within the function. The external variable is not affected.

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