c# - PInvoke & Delphi -

how can use dll function in c#? tried following error. "external component has thrown exception."

first time doing pinvoke stuff c# , delphi.

function httpget(location:string):string; stdcall; var http:tidhttp; begin   http := tidhttp.create(nil);   try     result := http.get(location);     freeandnil(http);   end; end;   exports   httpget;  begin end.   namespace test {     class program     {         [dllimport("project1.dll")]         public static extern string httpget(string location);          static void main(string[] args)         {            console.writeline(httpget("http://www.reuters.com/"));         }     } } 

you cannot call function c#. that's because cannot use delphi string interop. can use pansichar strings passed managed unmanaged, in other direction it's more complex. you'd need allocate memory @ caller, or use shared heap. prefer latter approach easiest done com bstr. widestring in delphi.

as has been discussed before, cannot use widestring return value interop, since delphi uses different abi ms tools return values.

the delphi code needs this:

procedure httpget(url: pansichar; out result: widestring); stdcall; 

on c# side write this:

[dllimport("project1.dll")]  public static extern void httpget(     string url,     [marshalas(unmanagedtype.bstr)]     out string result );      

if want unicode url use pwidechar , charset.unicode.

procedure httpget(url: pwidechar; out result: widestring); stdcall; .... [dllimport("project1.dll", charset=charset.unicode)]  public static extern void httpget(     string url,     [marshalas(unmanagedtype.bstr)]     out string result );