CAST

• Source: https://www.freebasic.net/wiki/wikka.php?wakka=KeyPgCast
• Last revised: 2019-07-04

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Converts an expression to a specified data type

Syntax

` Cast( datatype, expression )

`

Parameters

datatype

a built-in data type (standard type)

expression

a variable of another built-in data type

Description

Converts expression into a different datatype. Useful to be used in macros when datatype is unknown and also when converting to Type Alias.

This is a general form of conversion operators such as Cint or Cdbl.

Cast is more versatile because it can be used on built-in types that have a built-in Cast operator, but don't have a built-in keyword for it: e.g. Cast( Byte, boolean ).

It is also suitable for use in cases where the type of a variable is not fixed in the code - for example, it might be Defined earlier, or may be the Type of a different variable or expression.

Note: If you want to use an operator specifically for converting to different types of Pointers, consider using Cptr instead.

Upcasting: In an inheritance structure, the upcasting is converting a derived type reference or pointer into a base type.

In this special use, Cast applied on a derived-type instance (expression) can be used to return a base-type (datatype) reference.

By using a member Operator Cast, Cast can be overloaded for a user defined type expression.

Examples

start GeSHi

'' will print -128 because the integer literal will be converted to a signed Byte
'' (this Casting operation is equivalent to using CByte)
Print Cast( Byte, &h0080 )

'' will print 3 because the floating-point value will be converted to an Integer
'' (this Casting operator is equivalent to using CInt)
Print Cast( Integer, 3.1 )

Sleep

end GeSHi

start GeSHi

'' macro sizeofDerefPtr(): returns the size of the dereferenced pointer
#define sizeofDerefPtr(ptrToDeref) SizeOf(*Cast(TypeOf(ptrToDeref), 0))

'' macro typeofDerefPtr(): returns the type of the dereferenced pointer
#define typeofDerefPtr(ptrToDeref) TypeOf(*Cast(TypeOf(ptrToDeref), 0))

' Allocate dynamically memory for a Double by New
Dim As Double Ptr pd
pd = New typeofDerefPtr(pd)
*pd = 3.14159
Print *pd

' Allocate dynamically memory for a Zstring*10 by Callocate
Dim As ZString Ptr pz
pz = CAllocate(10, sizeofDerefPtr(pz))
*pz = "FreeBASIC"
Print *pz

Sleep
Delete pd
Deallocate(pz)

end GeSHi

Dialect Differences

• Not available in the -lang qb dialect unless referenced with the alias __Cast.

Differences from QB

• New to FreeBASIC

See also

• Cast (operator)
• Cptr
• Cint
• Typeof
• Coercion and Conversion

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