CODEWITHSUNDEEP
c#dlldllimport
Majak
Majak

Reputation: 1633

Making C# library using native Windows API

I am building C# library (.dll), where some classes use native Windows API functions. To be specific, functions GetPrivateProfileString and WritePrivateProfileString, like:

static class NativeMethods
{
    // external functions for working with ini files
    [DllImport("kernel32.DLL", EntryPoint = "GetPrivateProfileStringW",
      SetLastError = true, CharSet = CharSet.Unicode, ExactSpelling = true,
      CallingConvention = CallingConvention.StdCall)]
    public static extern int GetPrivateProfileString(string lpAppName, string lpKeyName,
      string lpDefault,
      string lpReturnString,
      int nSize,
      string lpFilename);

    [DllImport("kernel32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
    public static extern bool WritePrivateProfileString(string lpAppName,
                                                        string lpKeyName,
                                                        string lpString,
                                                        string lpFileName);
}

And using them:

NativeMethods.GetPrivateProfileString(section, key, "", result, 127, this.path);
NativeMethods.WritePrivateProfileString(section, key, " " + value, this.path);

When I am using this class directly in another project (without using it from dll), it works without problem. But when I build it into dll, then reference this dll in another project, then these functions aren't working. They simply do nothing.

Upvotes: 1

Views: 764

Answers (2)

Majak
Majak

Reputation: 1633

Oh, I found error. I forced to find ini file path in current directory (in my DLL class code). As I call it from DLL, it was automatically looking for file in C:\Windows. After using Directory.GetCurrentDirectory() + iniFile , it works.

Upvotes: 0

David Heffernan
David Heffernan

Reputation: 612794

Your pinvoke for GetPrivateProfileString is wrong as Matthew says. You need to use StringBuilder when passing string data back to the caller.

You are not checking for errors. So it's entirely plausible that the functions are failing without you knowing that.

In order to know why your calls are failing you'd first need to fix these issues. Then you can look at the return values. Knowledge also of the values of the parameters that you are using would help. But only you have the ability to do that, at present.

The bigger problem is that you are not meant to call these functions at all. The documentation says:

This function is provided only for compatibility with 16-bit Windows-based applications.

These functions contain numerous compatibility shims that make using them a complete minefield. Don't go there. Find a decent third party native C~ ini file class and pretend you never heard of GetPrivateProfileString and WritePrivateProfileString.

Upvotes: 1

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