Send an array of strings from vfp to a dll created on delphi

Question

I've created a DLL in Delphi that has to receive among other parameters, an array of strings from Visual Fox Pro.

I've tried different ways to send the data, but usually what i get is a "Declare DLL call caused an exception", and I'm not sure if the problem is the type of variable I'm sending on VFP or the type I'm receiving on Delphi.

We've tried sending an array of strings from VFP

Local arString[3]
arString[1] = 'Text1'
arString[2] = 'Text2'
arString[3] = 'Text3'

Declare integer callDLL in (dllfile) string, string, string
CallDLL('firstvar', 'secondvar', arString)

and on Delphi:

type Str: Array[1..3] of string;
function CallDLL(firstvar, secondvar: PAnsiChar; S: Str):Integer; stdcall ;
begin
ShowMessage(S[0]) ;
...
end;
exports CallDLL ;

Before I added the array of strings, the DLL worked correctly, so it's not the overall construction of the other parameters.

Any idea of what I'm doing wrong?

Thanks, TZ

It seems there is no array type parameter available, so you will most probably need to concatenate those strings on the FoxPro side and parse them on the Delphi side. Also, you have declared that the function will return an integer, whilst on the Delphi side you don't return anything. — TLama
– TLama, Commented Dec 12, 2013 at 13:09

David Heffernan · Accepted Answer · 2013-12-12 13:46:41Z

1

The simple bits first:

Your Delphi function needs to return an integer.
The string parameters are wrong. Delphi string is a managed private Delphi type. Those params should be PAnsiChar, pointer to null-terminated B bit character array.

Now to the string array. From @TLama's link it appears that arrays cannot be marshaled. So, you'll have to concatenate them, perhaps using double null-terminated strings. Or call the function multiple times and allow the DLL to collect the strings into an array or list.

answered Dec 12, 2013 at 13:46

David Heffernan

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3 Comments

ThadiusZho Over a year ago

Heh, sorry about that, I posted my question using code from memory. Both simple bit situations were already correct. I'll update the question to fix my mistakes. I'm trying the concatenated list and will report more.

ThadiusZho Over a year ago

Concatenating the string worked. Thanks, David and thank you TLama. I think I can't +1 a comment, but thank you nevertheless

Remy Lebeau Over a year ago

Passing the contents of an array as a single concatenated string is actually a documented requirement: "If the data you're working with in Visual FoxPro is in an array, you must loop through the array and concatenate it into a single string representing a C-style array before passing it to the DLL function.".

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