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Visual Basic Code > Convert a pointer to a string into a string

Convert a pointer to a string into a string

There are various instances (generally when using APIs) where it is necassary to convert a pointer to a string, back into a string. The following function returns a string from a pointer (a demonstration routine is at the bottom of this post):

Option Explicit

Private Declare Sub CopyMem Lib "kernel32" Alias "RtlMoveMemory" (pTo As Any, uFrom As Any, ByVal lSize As Long)
Private Declare Function lstrlenW Lib "kernel32" (ByVal lpString As Long) As Long


'Purpose     :  Converts a pointer to a string into a string.
'Inputs      :  lPtr            A long pointer to a string held in memory
'Outputs     :  The string held at the specified memory address
'Notes       :  
'Revisions   :

Private Function StrFromPtr(ByVal lPtr As Long) As String
    Dim lLen As Long
    Dim abytBuf() As Byte

    'Get the length of the string at the memory location
    lLen = lstrlenW(lPtr) * 2 - 1   'Unicode string (must double the buffer size)
    
    If lLen > 0 Then
        ReDim abytBuf(lLen)
        'Copy the memory contents
        'into a they byte buffer
        Call CopyMem(abytBuf(0), ByVal lPtr, lLen)
        'convert and return the buffer
        StrFromPtr = abytBuf
    End If
End Function

'Demonstration routine
Sub Test()
    Dim sTest As String
    sTest = "Andrew"
    Debug.Print StrFromPtr(StrPtr(sTest))
End Sub