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Appendix E - String Expressions   appendix



String Expressions

A string expression is anything that can be evaluated as a string of 0 to 255 ASCII characters. A string can be expressed in any of the following ways:

I. Simple Expressions
II. Compound Expressions

A compound string expression is a list of simple string expressions separated by the concatenation operator, "+". The syntax of a compound string expression is:

simpleExpr1 + simpleExpr2 [+ simpleExpr3 ...]

The "+" operator builds a longer string by concatenating the operands. For example, consider this expression:

"Ex" + "tra" + mid$("fiction",3)

This expression has the value, "Extraction".

Note: When two string expressions are separated by a data-comparison operator, such as: =; <; >, the result is a numeric expression. See Appendix D - Numeric Expressions, for more information.

Note: Because the dollar sign ($) is used to designate a full 255 byte pascal string, FutureBasic must determine what you really intended to use when you dimensioned a variable. The following examples demonstrate FutureBasic's evaluation methods:

dim as Str31 z 'z is a 31 byte string
dim z$;32 'z is a 31 byte string
dim z$ as Str31 'z is a 31 byte string
dim z as Str31 'z is a 31 byte string

dim as Str31 z$ "$" 'does not work. The $ overridces Str31.

Note: String length errors are not reported. Instead, strings are silently truncated to the maximum length that will fit in the destination variable.


Alternative syntax for fn CFSTR()

There is a new syntax, borrowed from Objective-C, for obtaining a CF string from a string literal. In most cases the new form @"foo" is interchangeable with fn CFSTR( "foo" ), but there are differences. @"foo" uses Apple's official CFSTR macro, whereas fn CFSTR( "foo" ) uses a CFSTR emulator in the runtime. The advantage of the '@' form is that it allows escaped characters (preceded by a backslash).

dim as CFStringRef cfstr
cfstr = @"printable ascii" // same as fn CFSTR( "printable ascii" )
cfstr = @"item 1\ritem 2" // embedded return char; same as fn CFSTR( "item 1" + chr$( 13 ) + "item 2" )
cfstr = @"\"" // double-quote char; same as fn CFSTR( """" )
cfstr = @"ƒøµ" // non-ASCII chars; don't do that! Instead use fn CFSTR( "ƒøµ" )


The '@' form requires a string literal (not a string expression).