Operator [] (String Index)operator

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

Operatorsoperatordocumented

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

Name		Description
`lhs`		The string variable or a string reference (not for example a constant or a string returned as a local copy).
`rhs`		A zero-based offset from the first character.
`T`		The wide-character type (varies per platform).

Description

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

For a String or a ZString:

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

For a WString:

a numeric type depending on platform, for example UShort for Windows or ULong for Linux (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

Example

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!

Reference

Documented in KeyPgOpStringIndex.html