I'm in the process of rewriting an overengineered and unmaintainable chunk of my company's library code that interfaces between C# and C++. I've started looking into P/Invoke, but it seems like there's not much in the way of accessible help.

We're passing a struct that contains various parameters and settings down to unmanaged codes, so we're defining identical structs. We don't need to change any of those parameters on the C++ side, but we do need to access them after the P/Invoked function has returned.

My questions are:

1. What is the best way to pass strings? Some are short (device id's which can be set by us), and some are file paths (which may contain Asian characters)
2. Should I pass an IntPtr to the C# struct or should I just let the Marshaller take care of it by putting the struct type in the function signature?
3. Should I be worried about any non-pointer datatypes like bools or enums (in other, related structs)? We have the treat warnings as errors flag set in C++ so we can't use the Microsoft extension for enums to force a datatype.
4. Is P/Invoke actually the way to go? There was some Microsoft documentation about Implicit P/Invoke that said it was more type-safe and performant.

For reference, here is one of the pairs of structs I've written so far:

C++

/**
    Struct used for marshalling Scan parameters from managed to unmanaged code.
*/
struct ScanParameters
{
    LPSTR deviceID;
    LPSTR spdClock;
    LPSTR spdStartTrigger;
    double spinRpm;
    double startRadius;
    double endRadius;
    double trackSpacing;
    UINT64 numTracks;
    UINT32 nominalSampleCount;
    double gainLimit;
    double sampleRate;
    double scanHeight;
    LPWSTR qmoPath; //includes filename
    LPWSTR qzpPath; //includes filename
};

C#

/// <summary>
/// Struct used for marshalling scan parameters between managed and unmanaged code.
/// </summary>
[StructLayout(LayoutKind.Sequential)]
public struct ScanParameters
{
    [MarshalAs(UnmanagedType.LPStr)]
    public string deviceID;
    [MarshalAs(UnmanagedType.LPStr)]
    public string spdClock;
    [MarshalAs(UnmanagedType.LPStr)]
    public string spdStartTrigger;
    public Double spinRpm;
    public Double startRadius;
    public Double endRadius;
    public Double trackSpacing;
    public UInt64 numTracks;
    public UInt32 nominalSampleCount;
    public Double gainLimit;
    public Double sampleRate;
    public Double scanHeight;
    [MarshalAs(UnmanagedType.LPWStr)]
    public string qmoPath;
    [MarshalAs(UnmanagedType.LPWStr)]
    public string qzpPath;
}