Data types overview

In 4D, data are handled according to their type in two places: database fields and the 4D language.

Although they are usually equivalent, some data types available at the database level are not directly available in the language and are automatically converted. Conversely, some data types can only be handled through the language. The following table lists all available data types and how they are supported/declared:

Data Types	Database support(1)	Language support	Variable declaration
Alphanumeric	Yes	Converted to text	-
Text	Yes	Yes	C_TEXT, ARRAY TEXT
Date	Yes	Yes	C_DATE, ARRAY DATE
Time	Yes	Yes	C_TIME, ARRAY TIME
Boolean	Yes	Yes	C_BOOLEAN, ARRAY BOOLEAN
Integer	Yes	Converted to longint	ARRAY INTEGER
Longint	Yes	Yes	C_LONGINT, ARRAY LONGINT
Longint 64 bits	Yes (SQL)	Converted to real	-
Real	Yes	Yes	C_REAL, ARRAY REAL
Undefined	-	Yes	-
Null	-	Yes	-
Pointer	-	Yes	C_POINTER, ARRAY POINTER
Picture	Yes	Yes	C_PICTURE, ARRAY PICTURE
BLOB	Yes	Yes	C_BLOB, ARRAY BLOB
Object	Yes	Yes	C_OBJECT, ARRAY OBJECT
Collection	-	Yes	C_COLLECTION
Variant(2)	-	Yes	C_VARIANT

(1) Note that ORDA handles database fields through objects (entities) and thus, only supports data types available to these objects. For more information, see the Object data type description.

(2) Variant is actually not a data type but a variable type that can contain a value of any other data type.

Default values

When variables are typed by means of a compiler directive, they receive a default value, which they will keep during the session as long as they have not been assigned.

The default value depends on the variable type and category, its execution context (interpreted or compiled), as well as, for compiled mode, the compilation options defined on the Compiler page of the Database settings:

• Process and interprocess variables are always set "to zero" (which means, depending on the case, "0", an empty string, an empty Blob, a Nil pointer, a blank date (00-00-00), etc.)
• Local variables are set:

  - in interpreted mode: to zero
  - in compiled mode, depending on the **Initialize local variables** option of the Database settings:
      - "to zero": to zero (see above),
      - "to a random value": 0x72677267 for numbers and times, always True for Booleans, the same as "to zero" for the others,
      - "no": no initialization, meaning whatever is in RAM is used for the variables, like values used before for other variables.
  Note: 4D recommends to use "to zero".

The following table illustrates these default values:

Type	Interprocess/Process (interpreted/compiled), Local (interpreted/compiled "to zero")	Local compiled "random"	Local compiled "no"
Booleen	False	True	True (varies)
Date	00-00-00	00-00-00	00-00-00
Longint	0	1919382119	909540880 (varies)
Time	00:00:00	533161:41:59	249345:34:24 (varies)
Picture	picture size=0	picture size=0	picture size=0
Real	0	1.250753659382e+243	1.972748538022e-217 (varies)
Pointer	Nil=true	Nil=true	Nil=true
Text	""	""	""
Blob	Blob size=0	Blob size=0	Blob size=0
Object	null	null	null
Collection	null	null	null
Variant	undefined	undefined	undefined

Converting data types

The 4D language contains operators and commands to convert between data types, where such conversions are meaningful. The 4D language enforces data type checking. For example, you cannot write: "abc"+0.5+!12/25/96!-?00:30:45?. This will generate syntax errors.

The following table lists the basic data types, the data types to which they can be converted, and the commands used to do so:

Data Type to Convert	to String	to Number	to Date	to Time	to Boolean
String (1)		Num	Date	Time	Bool
Number (2)	String				Bool
Date	String				Bool
Time	String				Bool
Boolean		Num

(1) Strings formatted in JSON can be converted into scalar data, objects, or collections, using the JSON Parse command.

(2) Time values can be treated as numbers.

Note: In addition to the data conversions listed in this table, more sophisticated data conversions can be obtained by combining operators and other commands.