Operator [] (String index)


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

Syntax:
Usage:
result = lhs [ rhs ]
or
lhs [ rhs ] = value

Parameters:
lhs
The string (a string reference, not a string returned as 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.

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!

Differences from QB:
See also:
Back to Indexing Operators
Back to Operators
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