Using GetProfileString API in C#

try to declare the interop declaration:

[DllImport("KERNEL32.DLL", EntryPoint="GetPrivateProfileStringA",
CharSet=CharSet.Ansi)]
private static extern int GetPrivateProfileString (string lpApplicationName,
string lpKeyName, string lpDefault, StringBuilder lpReturnedString, int
nSize, string lpFileName);

you need to create a StringBuilder object before invoking it.

Also try with the example at this tutorial:
http://jachman.wordpress.com/2006/09/11/how-to-access-ini-files-in-c-net/

The problem I'm having is that the StringBuilder only contains a portion of what should be returned; it's being truncated.  The return value of the call is 559, but the StringBuilder only has about 50 characters.

Passing string rather than StringBuilder the return value is 0, and the string is empty.

I found what I needed in one of the comments below the article.  You need to pass a char[] instead of a StringBuilder.