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How to return a string of unknown size from DLL to Excel Visual Basic in C ?

  1. 03-14-2017, 04:42 AM #1
    u24c02
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    How to return a string of unknown size from DLL to Excel Visual Basic in C ?

    Dear All,

    Now I'm trying to receive the string return value from DLL to VBA.
    "C-DLL code "
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    and the below is the VBA code

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    when I ran above code, I've got receive well the d1 and d2 data but the problem is that "s" I can't get it.

    Is it possible to directly return the resulting string from the DLL? Or is there any other way to dynamically allocate a string object depending on the length of the result and return it to a VB caller?

    I tried different approaches, for example like this (ugly, just examples), but I can't get exactly the string value what I want.
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  2. 03-14-2017, 03:42 PM #2
    Bernie Deitrick
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    Re: How to return a string of unknown size from DLL to Excel Visual Basic in C ?

    Did you try
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    Bernie Deitrick
    Excel MVP 2000-2010
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  3. 03-14-2017, 05:15 PM #3
    xlnitwit
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    Re: How to return a string of unknown size from DLL to Excel Visual Basic in C ?

    Can you use a BSTR in your C code?
    Don
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  4. 03-14-2017, 05:26 PM #4
    Leith Ross
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    Re: How to return a string of unknown size from DLL to Excel Visual Basic in C ?

    Hello u24c02,

    I could be wrong on this but I think your string needs to be called ByVal and not ByRef. The reason is when a variable name is declared as a String type in VBA, the variable returns the address of the declared string's name and not the first byte of the string itself as it does in "C". If you pass the variable ByRef (by reference) you will pass the address of the VBA declared string's name. If you pass it ByVal (by value) then you pass the contents of the decalred string variable which is the address of the string itself.
    Sincerely,
    Leith Ross

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  5. 03-14-2017, 10:32 PM #5
    u24c02
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    Re: How to return a string of unknown size from DLL to Excel Visual Basic in C ?

    Quote Originally Posted by xlnitwit View Post
    Can you use a BSTR in your C code?
    As I know the BSTR can't use in the C.
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  6. 03-14-2017, 10:34 PM #6
    u24c02
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    Re: How to return a string of unknown size from DLL to Excel Visual Basic in C ?

    Quote Originally Posted by Leith Ross View Post
    Hello u24c02,

    I could be wrong on this but I think your string needs to be called ByVal and not ByRef. The reason is when a variable name is declared as a String type in VBA, the variable returns the address of the declared string's name and not the first byte of the string itself as it does in "C". If you pass the variable ByRef (by reference) you will pass the address of the VBA declared string's name. If you pass it ByVal (by value) then you pass the contents of the decalred string variable which is the address of the string itself.
    Thanks for your reply,
    Yes you are right. I'm supposed to have a ByVal.
    ThAnks
    Last edited by u24c02; 03-14-2017 at 11:46 PM.
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  7. 03-15-2017, 11:44 AM #7
    Leith Ross
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    Re: How to return a string of unknown size from DLL to Excel Visual Basic in C ?

    Hello u24c02,

    You're welcome.
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