LPCSTR data type equivalent in C#

Question

I have an API that takes three parameters:

HANDLE  Connect(LPCSTR MachineName, LPCSTR ServerName, BOOL EnableDLLBuffering); 

How can I use this method in C#?

What is the equivalence of LPCSTR? And what should be use in place of HANDLE?

Answer 1

The HANDLE equivalent is IntPtr (or you could use one of the subclasses of SafeHandle, many of which are defined in the namespace Microsoft.Win32.SafeHandles). The equivalent of LPCSTR is string or StringBuilder (but string is better, because you are passing the string to the method and the method won't modify it). You can even use a byte[] (as I have wrote you in the other response, but you must encode your string in the buffer, and add a \0 at the end... it's quite inconvenient). In the end an LPCSTR is a constant LPSTR that the method won't modify. It's better you set the CharSet.Ansi as in the other response.

[DllImport("YourDll.dll", CharSet = CharSet.Ansi)]
static extern IntPtr Connect(string machineName, string serverName, bool enableDLLBuffering);

and you call it as:

IntPtr ptr = Connect("MyMachine", "MyServer", true);

or, if you really want to do the encoding yourself:

[DllImport("YourDll.dll", CharSet = CharSet.Ansi)]
static extern IntPtr Connect(byte[] machineName, byte[] serverName, bool enableDLLBuffering);

and

public static byte[] GetBytesFromStringWithZero(Encoding encoding, string str)
{        
    int len = encoding.GetByteCount(str);

    // Here we leave a "space" for the ending \0
    // Note the trick to discover the length of the \0 in the encoding:
    // It could be 1 (for Ansi, Utf8, ...), 2 (for Unicode, UnicodeBE), 4 (for UTF32)
    // We simply ask the encoder how long it would be to encode it :-)
    byte[] bytes = new byte[len + encoding.GetByteCount("\0")];
    encoding.GetBytes(str, 0, str.Length, bytes, 0);
    return bytes;
}

IntPtr ptr = Connect(
                 GetBytesFromStringWithZero(Encoding.Default, "MyMachine"),
                 GetBytesFromStringWithZero(Encoding.Default, "MyServer"), 
                 true);

This variant is better if you have to call the method many many times always with the same strings, because you can cache the encoded versions of the string and gain something in speed (yes, normally it's an useless optimization)

Answer 2

According to How to map Win32 types to C# types when using P/Invoke?:

• LPCSTR (C) - string (C#)
• HANDLE (C) - IntPtr (C#)

Answer 3

I use StringBuilder:

    [DllImport("user32.dll", CharSet = CharSet.Ansi)]
    static extern int GetClassName(IntPtr hWnd, StringBuilder lpClassName, int nMaxCount);

    var sb = new StringBuilder();
    var ret = GetClassName(hwnd, sb, 100);
    var klass = sb.ToString();