Operator String Index

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Operator [] (String Index)

Returns a reference to the numeric value of a character in a string

Syntax

Declare Operator [] ( ByRef lhs As String, ByRef rhs As Integer ) ByRef As UByte
Declare Operator [] ( ByRef lhs As ZString, ByRef rhs As Integer ) ByRef As UByte
Declare Operator [] ( ByRef lhs As WString, ByRef rhs As Integer ) ByRef As T

Parameters

• lhs
• rhs
• T

Description

This operator returns a reference to the numeric value of a specific character in a string:

a UByte (containing the ASCII value of the character).

a numeric type depending on platform, for example UShort for Windows or ULong for Linux and macOS (containing the numeric value of the character).

This operator must not be used in case of empty string because reference is undefined (inducing runtime error).
Otherwise, the user must ensure that the index does not exceed the range "[0, Len(lhs) - 1]". Outside this range, results are undefined.

Unlike 'return by value' (where only a copy is returned), 'return by reference' allows you to also modify the referenced variable.
'Return by reference' is implemented under the hood as a pointer implicitly dereferenced:

- In case of a String or a ZString 's':

s[n] is equivalent to *CPtr(Ubyte Ptr, StrPtr(s) + n)

- In case of a WString 's':

s[n] is equivalent to *CPtr(T Ptr, StrPtr(s) + n)

Note: The fact that this operator returns a reference greatly differentiates it from Asc( str [, position ] ) which allows to return the numeric representation of a character, but not to modify it.

Remarks

Usage

result = lhs [ rhs ]

or

lhs [ rhs ] = value

Differences from QB

• New to FreeBASIC

See also

• String Operators

Examples

Dim a As String = "Hello, world!"

Dim i As Integer

For i = 0 To Len(a) - 1

    Print Chr(a[i]) & " ";

Next i

Print

Print

For i = 1 To 4

    a[i] = a[i] - 32  ' converting lowercase alphabetic characters to uppercase

Next i

For i = 7 To 11

    a[i] = a[i] - 32  ' converting lowercase alphabetic characters to uppercase

Next i

Print a

Will print:

H e l l o ,   w o r l d !

HELLO, WORLD!

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Category: Operators
Kind: operator

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Reproduced from the FreeBASIC Wiki Manual under the GNU Free Documentation License 1.3 — with no Invariant Sections, no Front-Cover Texts and no Back-Cover Texts. Copyright © the FreeBASIC project and wiki contributors. See License.